Stovebolt front axles are stiff and heavy enough that it's not practical to make side to side adjustments, so putting the same amount of shim at both sides is about the only option you have. Putting different caster shims at each side just bends the springs- - - -and short of getting the alignment checked by a professional shop, there's no telling what the actual angle will be. Ford axles on vehicles with a single transverse spring could be bent with the right fixtures and big bottle jacks to get an exact alignment. Not so with Chevy and other vehicles with two front springs and heavier-made axles.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!