Drilling rear drums

And to answer the original question. “Yes” you can drill your original drums but my suggestion is to drill them in between the factory holes and not oblong the originals. Knock your current studs out of the axle and center it and mark holes and drill. My 72 Demon has Mosier axles at the 5x 4.500” 1/2” studs but set up for factory brake backseat so the original drums work. Machine shop did the holes for me.