1971 Demon Rear end upgrade

Hemillama said
The question is really more disc brake related, Dr Diff does not know if the disc they sell will work with the 6.5 backspace of my wheels

Lots of careful measuring unless you want to install and do a mock up. It's a roll of the dice to find someone out there with the same car, rear end with disc brakes, and the offset wheels you have. What did that rear end come out of?