Transmission fluid has a specific temperature where it flames up. I don't know what that specific temperature is, but I stopped when it reached that temperature and moved on to the next cylinder, so's on and so's forth's until complete.
These are cast iron pistons by the way. I probably wouldn't go that hot with aluminum pistons if I thought that they might be salvageable.
I let the engine sit for days after boiling the oil, more based on defeatism than an actual plan. Low and behold, it freed up.
Once I got it to move the pistons down, I poured mineral spirits into the cylinders when they were at the bottom of their stroke, then used a maroon Scotch Brite pad soaked in the mineral spirits to remove the gunk on the tight spots. That really helped in getting it spinning by prying on the flywheel teeth.
