9" drum hub drill to BBP?

Unless you're building a drag race only car, throw those 9 inch drums in the scrap pile. They may have worked in the late sixties, but will not stop you fast enough when the soccer mom in front of you slams on her four wheel discs because her kids are fighting over the DVD remote control. Lots of better options available now. From the cheap Scarebird kit all the way up to Wilwood kits.

X2
There is a reason for the 9X3 drum brakes being found on slant 6 a-body only. You can buy modern, more aggressive brake linings today.
Actually, you don't have a choice since the OEM asbestos was outlawed.
Those will just wear the drums faster. Have you searched for new drums lately ? Good luck with that.