You need parts (new and old) in hand and measure to make those decisions.
It'd be a bummer to guess wrong on the hole size and not have the studs fit when you finally got them.
You can even do a test hole in something else and see how one fits before modifying drums/hubs.

Before any of that be sure you can't find the originals first.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-