If it were me, I would ditch all of the aftermarket stuff, get a manual drum/drum master for a 69 Dart, which is the same unit as manual disc, and go back to the stock setup. The pushrod would be easy to source right here, I have a couple laying around. This is exactly why I prefer the factory setup on things, with aftermarket stuff you just get too far from the barn to make sense of it all. When it’s factory, or near factory, you can use the service manual, source stock parts from here or most auto parts stores, and avoid the hokey pokey of some other less informed shade tree mechanic that couldn’t get it right either. Sorry to hear that you’re struggling, as Mopar brakes are so easy to work on, but as you’ve found out, those pets are not Mopar, or probably not even compatible with your stock drums.