best way is to use a 4 bolt to 2 bolt adaptor on the firewall and use a newer style 2 bolt alum MC from mid 80s car/truck
gives much more room with the BB in A-bodys
dr diff sells a nice adaptor,MP sells one,you can even get an offset one for a hemi in an A-body
I used the mp adaptor and adjustable brake rod from master power brake
used the 73 manual disc brakes with 11x2.5 rear drums on my 68 Dart
I used the stock 2 bolt alum MC off the power brake set up on my 88 truck and made my own 4 bolt to 2 bolt alum plate for firewall support to go manual brakes,manual steer,manaul shift with the 440 in the truck