The "Total-Contact" dual-leading-shoe brakes used on your '61 are a strange design by recent standards (using
two wheel cylinders per wheel, for instance) but they do offer reasonably low pedal effort when in good repair. I mention this because if you are experiencing high pedal effort, it suggests that the brake system probably wants a good, careful inspection, especially if the car has been sitting and/or neglected for awhile (which seems probable, given the other issues you're experiencing with the cooling system, wiring, etc.). Power brakes were available in '61, but the system was rather primitive and complex, and the original parts will be difficult and expensive to get.
It sounds like you are probably at a point where you would want to think more generally about brake upgrades, figure out what you want the end result to be, and work backward from there.
You may also want to spend some time looking at
this site (extensively upgraded and modernised 1960 Dart) and possibly start a conversation with the car's owner. Note he swapped in more modern brake equipment, including a power booster.
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