I'm getting ready to install a Scott's IFS (1st attempt at IFS) on my 59. Shouldn't the axle centerline be a known measurement?

For example;

1) Heidt's & TCI say to measure 20-7/8" from the front shackle bolt centerline.

2.) Jim Meyer Racing say to measure 26-7/8" from front of frame.

3.) Scott's say to get the centerline from the stock king pins. This doesn't make sense to me because there is no weight on the suspension. With weight the axle would move forward and w/o weight the axle will move back.

4.) No Limit says the centerline is the 1/2" hole on top of the frame. They also recomend moving it forward 3/8" to center the wheel in the opening.

Thanks

Don't go by the front of the frame, as 55-57 vs 58/59 are different.

I'd plumb over the axle then move forward. If you don't move forward, the wheels appear to be set back on the fenders. I think 3/8ths is too small though, my buddy I helped moved his 1.5 inches, but his was sitting way down (F-body clip) with a bit of rake. It made the tires look real nice in the wheel wells.

I'm sure you get more info soon.

i plumb bob'd mine, and it is right around where the holes are. i plan to move it forward 1" (maybe 1.25") with a nova clip.

its here

It looks like from the pictures that if I move the CL about 1/2" forward of the 1/2" hole in the top of the frame will get my wheels centered in the fenders. Is this correct?

I suggest you tack it in place and then put the sheet metal and tires back on. If it looks good then weld it up.