Hi greendart.
Like you,I also have a 70 Dart with drums all around. I got lucky though and found a freshly wrecked donor car. Brakes were all brand new but the young driver had rolled the car into a field and totalled it. Plus the younger fella that bought it for parts only wanted the drivetrain. So I stole the entire set up for $125. Booster,master lines,propotionng valve, spindles,bearings ,calipers,rotors, etc etc etc.
And it's small bolt pattern 4 piston kelsey hayes,so I dont need to redrill the rear axles for LBP. Factory rims will work etc..
I'd say this is the most straight forward deal as it's simply bolt on and there is no changing control arms or bolt pattern. However,they can be a maintenance pain,but...
I plan on having my calipers and master rebuilt by SSBC so they should perform much better. KH 4 pistons have a tendency to stick when the car sits for a while,but this is easily solved by using silicone brake fluid. The shelf upon which the pads ride tends to get worn with grooves in hi mileage cars,but this can be welded up and then filed smooth.
The later calipers from A bodies will work,but this changes your bolt pattern,which is a plus if you want better rim selection. Later brakes also tend to be lower maintenance. Only disadvantage being you need to drill the axles or replace with LBP axles,just so you have a matching bolt pattern all the way round.
I believe you need to change the upper control arms for later brakes,so whichever donor car you find,grab them as well.
