Kips41,
those shims that they are selling are pretty useless. I ran into the same thing and made my own. You should have multiple shims of .002" each. I would be starting with three .002s on each side. I think bolting it down with no shims to start wil make sure that the shells are seated properly.

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!