OK, small update... I haven't tried the Evaporust yet, but the two flavors of ATF and the PB Blaster have results. After a couple days soaking, I held the rod big ends in a vice and smacked the pistons with a plastic dead-blow hammer and they all started to move. I would say that the the ATF + mineral spirits moved the easiest, but none were going to move by hand after just a couple days. Also, as cdstl noted, the acetone does evaporate out pretty quickly. It doesn't mix like the mineral spirits do, so you need to stir it periodically and add more acetone from time to time - things I didn't do.

The PB Blaster was the slowest to loosen up, and had the most friction after the two-day soaking. However, after soaking all three for a few more days, all three loosened up enough to move by hand - after another round of dead-blow treatments. Pretty quickly, all three could be moved by hand, and the PB piston was actually the easiest to move, followed by the ATF+spirits, then the ATF+acetone.

So, given a week and some dead-blow persuasion, all three methods appear to work. I've got 5 more pistons to go, so I'll repeat these three again, and then do a pair with the Evaporust just to say I did. Maybe there will be a clear leader after that effort.