When you're buying shims for the axle, make sure you are getting solid machined shims not cast iron. The new cast iron ones are coming overseas and are as brittle as glass. I installed a couple in my 49 3600 (when I did my own T5/4.3 swap) and they cracked almost by looking at them. Found some machined ones and carried on.

1949 Chevrolet 3/4 Ton - Still Solid. Regular Driver
OT Vehicles:
1925 Hudson Brougham Super Six
1950 Chevrolet Styline (Parts)
1952 Canuck Pontiac Sedan Delivery (Well Underway)
1973 F250 4x4 Highboy
1977 F250 4x4 Lowboy