After honing my cylinders to remove the rust, I welded up a U shaped cradle that attached to the head bolts on My D2. I made the cradle high enough to put a small bottle jack with a 3.950 diameter round slug under it & on top of the piston. This allowed me to put pressure on the top of the piston and gently push down. Every day for a week I added more PB blaster and pressure and she broke lose. However I did end up changing my rings as I had a couple broken.
Best of luck
Restored 1970 ford tractor,1931 Model A PU streetrod, lifted 1978 F150, 1971 VW bug, antique chain saws