68 Dart GTS brake problems

Sounds like you removed the MC to "bench bleed". Many take that term too literally. I always install the MC on the car and bench bleed using the pedal. It may take 50 strokes to get all air bubbles out. I also don't like the plastic bleeder fittings since they can suck air past the threads, or the push-in type can pop off. I try to keep bent metal tubes for bleeding. If your existing MC was original, it suggests the car had factory front disk brakes.

Install the drums w/ shoes fairly loose, so they don't drag. When you first test drive, back up many times in a parking lot, jamming the brakes hard each time so the self-adjusters do their thing. The pedal should start taking less motion. I use DOT 5 in most my cars. I was afraid a wag would state the oft-claim "silicone is spongy". But, do carefully pour it in down the side of a funnel so it doesn't entrain air bubbles, since they take longer to settle out in silicone.