Been doing more research on this hub sizing problem, haven't been able to make heads or tails of why they (aftermarket) would change something so standardized as the register hub.
I have a pair of basic street/strip c-clip style Strange axles ready to go into the `67 dated 12 bolt, and the registers on them fit the drums just fine.
Here's the same drum on the HD axle:
Luckily, the wheel register clears with room to spare, and I didn't even have to drill out the axle stud holes, there's already ample room for the 1/2' studs (note the wheel is slipped directly over the axle flange, the drum is not in place here):
We'll see what Strange has to say tomorrow.