If everything else seems to fit OK- - - -like the center hole of the new drum being the proper size to align with the hub, and the depth of the drum fitting the backing plate properly, I'd suggest drilling and tapping for a couple of flat head screws to hold the drum to the hub securely, and just live with the short engagement of the knurl in the drum. Finding a stud with a taller knurled section shouldn't be difficult- - - -find a Dorman products paper catalog and a parts store counter man who knows how to read it, which may be the most difficult part of the project!
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!