my suggestion is to start at the front and work back, the master cylinder mounting and correct operation is far more difficult than the caliper mounting
IF ... you can fabricate what is needed to mount the master cylinder to the frame, either bolt on or welded, weld an extension to the cable brake pedal, or use a 03+ peg/pedal, and align all that correctly during fabrication to properly operate the master cylinder, the rear caliper bracket is the easy part.