Order a new MC for a 73-76 power disc brake car from any ordinary parts store but run it manually. No need for power brakes unless you are physically limited. This will get you a 7/8 bore and it bolts right in place. Use the pushrod from your existing setup. You will have to fab or buy brakes lines for the MC. I've done this 3 times and you'll love the brake feel with your new K-H discs. No need to get fancy here.