It would be best with the bleeder open, but then you will need to bleed the system with a power bleeder. My thought was some build up in the cylinder that may be restricting motion.

 

My thanks out to MudManiac: Holla! You helped get me on track with the rear caliper pistons. I took one apart, found it to be badly corroded and uncooperative, got a near new set of rear calipers from the wreckers for a good price (pads almost new; calipers still semi-shiny; lines in good shape; couplings all good), installed them, and I'm off to the races... so to speak.

My thanks to all the members who took time to help out.

 

Thanks for keeping us updated, I'm glad you figured it out.