Front brakes won't release

You should have put this in your other thread. The brake pedal does not always tell you. Loosen and or REMOVE the master from it's mount to make sure the piston is fully returning

Did cracking the line fittings IMPROVE the release?

I know you claim this is a correct cylinder but in this day and age I would suspect ANYTHING. Make CERTAIN whichever end of the master the fronts are connected to do NOT have residual valves. You should be able to tell by gingerly probing with a small nail / brad. I would clip the point and then grind / sand the nail to a flat/ rounded end.

If it's a restriction in the tube system the ultimate test would be to have someone pressure them up, then release a bleeder at one caliper

Other than that are these rebuilt or new? If rebuilt, "suspect."

ALSO I am not familiar with the pads on these later brakes. Are they similar to the 73 brakes? If so, READ THE factory manual. Some pads need to be "seated" with a mallet. They can bind and maybe cause the piston to bind.