I haven't been there yet but if you shim the front by some amount, it is really pivoting on the back shackles, I would think. Therefore because the fenders add another 3 1/2' or so, I would expect the core support to need twice the shim depth.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!