Do you have the Chevrolet Factory Repair Manual? It will guide you through the process.
This is all that I could find in the Shop Manual - 1948-1951(, but probably good for radiator through 1953? It does not discuss/describe using shims (metal or "fabric). I have used such shims (and, used too many). Someday, I'll re-adjust the "front clip" (it sits too high on my Suburban).