A153 ssbc conversion?

A whopping $985 at Summit. The A153 kit uses Kelsey-Hayes calipers, but apparently a custom integral rotor/hub. I don't see a price for the new rotors you will eventually need. I hope not priced like ink-jet cartridges. The MC is an old cast-iron factory one if you like that look (rusty) and weight. They don't state the bore. A 7/8"D would give a workable pedal without too much travel (if no air bubbles and good hoses).

If you get a manual brake rod from a 69 Dart (someone here), it should fit their MC since they say the kit works on power or manual cars. You will need a new rubber bushing for the end.

Since happy with your 10" drums, why not install another booster, the cheap way. I have a booster/MC from a 95-99 Breeze w/ ABS on my 65 Dart (~$25 junkyard). Look at my avatar. I had to elongate the Dart bracket's holes slightly and use dual nuts, but that was simple. I used 1974 Dart firewall brackets, which could vary from your 1969's. Probably many other boosters would work, I just tried the closest car.