Bolt a piece of 2" square tubing across the top of the cylinder with a couple of head bolts, and use a piece of 3/4" all thread rod and a nut welded to the tubing to put some down pressure on the piston. Tighten the bolt against the top of the piston, smack the top of the threaded rod with a hammer a few times, "Rinse and repeat". Keep the cylinder well-soaked in penetrating oil while you're persuading the piston to move. Count on boring the engine oversize to get rid of the rust pits. I'd suggest putting a set of standard bore 235 aluminum pistons in rather than going back in with the heavy cast iron 216 pistons. The lighter weight 235 pistons have the same compression height and wrist pin size as a 216. You'll need to bore the cylinders .0625" oversize, which will clean up any deep rust pits nicely and give you 224 cubic inches in the process.
A 216 will have a 3 1/2" bore size, and a 235 will be 3 9/16". The stroke is also different on the 235. A quick measurement of a piston will tell you which engine you're dealing with.
Jerry
