Mark, I like Aero Kroil penetrant made by Kano Laboratories, it's been around before WWII. Getting some Aero Kroil inside the spark plug holes or between the pistons and the the cylinder walls after the head is removed along with giving the penetrant time to do it's work might at least allow for easier dis-assembly. I know some guys have their home brew of penetrant as well, i cannot remember what's been said to work well. Assuming the engine is not locked up from running out of oil (your story sounds like this is not the case) and if the bike sat on it's sidestand, most likely the #1 piston is "stuck" the worst, as water/condensation tends to run down hill.... I've had engines that were locked up, along with squirting routinely Aero Kroil into spark plug holes, i put it in 5th gear (i realize you may not be able put the transmission in gear, perhaps if you take of rear chain and try moving front sprocket back and forth you may be able to get the gears to engage) then i looped a cranking type tie down strap thru the wheel and frame, applying pressure to wheel to apply pressure to primary drive and to crankshaft. Periodically, i would loosen strap, rock wheel back and forth and then apply tension to strap again along with more Aero Kroil. With the one engine, after about 3 weeks of this treatment, things started turning. In the case of the other engine, began turning after a few days. Not being able to free the pistons from the cyl.walls, i have seen somewhere (on the internet) guys that submerge the entire engine in a penetrant bath, in order to free things up. I understand there are restorers who have use these penetrant baths for these "frozen" engine conditions. It's going to be pretty important to free the pistons in order to remove the cylinder without risking damaging parts.