Those cylinders are going to need to be rebored to eliminate the rust pits, so the pistons are junk. You can shorten the disassembly process by using a big hole saw in a low speed variable drill motor or a drill press, and cutting away the piston crowns just inside the piston ring diameter. 235's have a bore size of 3 9/16", so use a carbide-tipped hole saw about 3 3/8" in diameter and cut down just past the piston ring area, maybe 3/4" or so. Once that is done, hammer on the middle of the piston to break it away from the stuck rings.
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