[dsraven]

yup.
here's a pic of the 58 frame with the 57 sitting on top. this shows the rad support brackets moved, the old bracket holes and also the amount needed to cut off the frame horns. I have that dimension somewhere but can't seem to locate the pics.
what MII cross member are you thinking? I went with a TCI through a retailer here but was shipped the wrong cross member and got little to no help with dimensions etc. I ended up figuring it out myself to get the geometry right (lic'd mechanic by trade) but the truck sat lower than I wanted, that may have been from the mods required to the cross member but that would only account for a small amount, possibly 3/8-1/2". I went with the 2" drop spindles and a 235/75r15 (28.9" tall) tire, front and rear, for mock up. I moved the axle center line ahead about an inch and at my ride height, with the lower control arms level to the ground and a 2 deg rake angle, my rockers at the front of the door were about 6" off the ground.
gotta say, check what you are getting from any supplier. control arm tube thickness, ball joint quality, brake parts, shocks, stab bar ends etc etc. when assembled the rubbers on the ball joints were squeezed down and would be open on one side. not gonna last long. some ball joints and tie rod ends have a sealed rubber which is much better in my opinion. TCI has probably come along since then as this was about 10 years ago when I did that frame.
welders series has lots of brackets etc that may come in handy. I would advise a digital magnetic torpedo level for assembly and this can be placed across a longer level for frame side to side levelling etc. the torpedo level will help you get the control arms level etc.
the LS engine with a camaro oil pan, camaro engine mounts bolted to block and camaro exhaust manifolds fits well between the frame rails. let me know if you wanna see the pics, just pm me your email address.