55.2-59 1956 Do I need to notch?

[mr48chev]

I'm going to say yes with at least the notch like Dsraven showed . it took me a minute to figure that the brackets on the sides of the frame rails are for bags or coil springs. The notch over the axle and the boxing plates are what you are looking at. other than that it all depends on how low you plan to go and how much clearance you are comfortable with, You may have to have a raised notch over the axle if you intend to be real low but maybe not as much as the lay frame brigade.

The best I can offer is set your lower A frames level (most likely without springs installed. set the front static height at what you intend for it to be. then block the rear of the frame up at the height you intend to have it sit static at and start measuring.

If you don't have the tires or rollers that size that you intend to run you can use this calculator to figure out what the diameter of the tire is https://tiresize.com/calculator/ Then half the diameter plus half the axle tube diameter gives you the alleged top of your axle tube at static height. That will tell you where the axle is going to be in rellation to the frame rails.

Then you have to decide how much clearance between the frame rail and axle is "safe clearance" as there is no carved in stone measurement on that. All I can say on that is that not enough clearance means that the axle may and most likely will hit the frame rail at times.

I'm not intending to suspend my 48 on bags but plan to run a pair of bags as load leveling bags controlled by a level switch that was used on a lot of Cadillacs over the years with air shocks. That way static height will always be the same in theory.

[dsraven]

It is very important to have your tire diameter that you intend to be final with when you are mocking up. Stop at a tire store and get some scrap tires or something that holds air that's the size you want to run. If you buy tires and it takes you a few years to get your truck finished the tires may be outdated by the time you end up getting finished. Haha. Anyway, very important to have the right size tires on when you're mocking it up otherwise if you decide to change tire sizes then maybe the rake angles are wrong and the front end alignments out of whack etc etc

[BigDaddyK]

Appreciate all the replies. I'll take it all in at this point. I haven't decided on Tire size etc. yet. It is on my radar though, but I figured I might as well get the IFS installed and the rear end built (the 8.8 was not posi and 28 spline. I want 31 spline and obv. posi).

[dsraven]

you really should decide on a tire diameter for front and rear and a arke angle for the frame before you install an IFS. this is because the IFS needs to be installed with the lower control arm pivot shafts positioned so they are level, front to rear, and the lower control arms themselves should be set up so they are level, side to side, when at ride height. if you install the same diameter tire on the front and rear then it becomes more of a rake angle issue for setting up the IFS for welding in. if the IFS cross member isn't welded in to keep the geometry correct for the rake angle and tire diameters you plan to end up with then it will be difficult or impossible to set the alignment correct when done.
another thing to consider for a task force truck is that the front fender wheel openings are not symetrical on the front and rear side of the wheel. the rear part angles in such a way that if the axle centerline and tire diameter are not considered and possibly mocked up beforehand you may end up with a set up that looks like the front tires are not centered in the wheel openings. as the truck is lowered the tire generally looks like it is too far towards the rear of the wheel opening. the further the truck is lowered the more exagerated this looks. generally I think most lowered TF trucks set the axle centerline about 1.5" ahead of the stock placement. less lowering would equate to less centerline adjustment.
when ready to start work on the frame I suggest to set the frame up on some sturdy stands and adjust the stands so you get the rake angle you want and also ensure the frame is level side to side. I suggest using a digital level for this because it will give you a screen to read the angle instead of a bubble betwwen 2 lines. a good bubble level is accurate enough but can be decievingly read if you are not looking at the window straight on. the digital level will say the same from whatever angle you look at it from. when setting up the stands try to place them where they wil be out of the way but also not allow the frame to move when dropping out the old front end parts. before installing the new parts recheck the frame angles to be sure things are still where you want them
what I have found to work well is a set of good sturdy jack stands, mine are 6 ton ones, that have a good wide base. I removed the pull up part and tack welded a flat plate across the opening. the plate had a hole drilled large enough to allow 3/4" threaded rod to slide through. then a nut was welded on top of the plate so the threaded rod could be threaded into the top of the stand where the adjustable part used to slide up and down. an extra nut was spun onto the threaded rod to act as a jam nut and keep the threaded rod locked in place at the desired height setting. on the end of the threaded rod that would contact the frame i welded a smaller bolt, like a 3/8 x 1. that smaller bolt fit into a hole in the frame and was held with a nut to ensure everything was locked down once set up how i needed it. this allowed for some very small adjustments to be made during frame levelling and rake angle set up.
I purchased digital torpedo level for a decent price and used my 4ft aluminum bubble level as a longer straight edge to set the torpedo level on so it could span the frame rails. the nice thing about the torpedo level is it is quite handy when checking the angles on things like control arms and other smaller items. it has a magnetic base so it can hang on things while you adjust parts to get the angles you need before tacking things up.
in my case i used the longer level to span the lower control arm pivot shafts, which I installed in their places but left protruding on the front side far enough so that the long level couls span their width. this allowed me to get the side to side levelling done acurately instead of relying on the formed metal crossmember, which may or may not be level when the pivot shafts are level. for the fore to aft check a longer shaft could be used so it protrudes further on the front side to allow the torpedo level to sit on the shaft, or a longer shaft could be used for mock up. this negates the need to assemble, dissassemble, assemble, dissassemble during the set up prior to welding
I highly recommend to get familiar with how an IFS system works so you know what to look for when setting up the new cross member. heidt's used to have a write up in their tech section called "understanding IFS" and it quickly told the most important things to look after and ensure they are right before burning in a cross member. there are other more in depth articles online as well. if not done correctly you could easily end up with bump steer (which changes the steering angles as you go over a bump) or angles that can't be adjusted correctly for good alignment and driveability. you don't wanna end up with a truck that has to be herded down the road, constantly floowing every crack in the pavement or has a ywitchy feel that makes you constantly tend the wheel.
anyway, post up your progress when you get started and ask questions as you go if you need help. lots of knowledge on here if you just ask.