http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0585.htm
I don't think the original shims were that thick.
In my area I go to a shop that does straight axles for big trucks.
They do 1/2 tons as well.
The first check, for an old unknown truck, is to make sure the axle is not bent.
Then check that the camber is correct.
Shops that do this kind of work day-in and day-out know what to look for.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."