Hard pedal

Which front discs do you have? The MC with the same sized reservoirs is wrong for both the Mopar 73-76 fronts discs, and for the Kelsey Hayes ones. It should work to make the brakes stop, however.

If your calipers were hard to push in, they very well may have rust in the bores. This is fairly common on the single pistons types. And yes, sometimes if the piston bores are rusty, the pistons will get stuck in the bottoms of the bores, and not move. I'd be pulling them apart. It might be pretty hard if you don't have the MC hooked up. Single piston rebuilt calipers are not all that expensive. If you do decide to pull yours apart, and the pistons are stuck, you will need a special piston wrench. If you rebuilt your self, get ALL the rust out. If the bores are heavily pitted then the chance of success goes down.