How many hours does the engine have on it at the moment? If the bearings look good, and the clearances pan out OK with a Plastigage check, I see no reason to replace them. All new gaskets and seals, of course! Replacing the rings is just about a necessity, because they will have to establish a running fit with a new block. Is your replacement block standard bore, and straight enough in the cylinder walls that it won't require a rebore and new pistons? My rule of thumb has always been no more than .003" taper wear in the cylinders before I insist on a rebore. Be sure to do a good glaze-breaking job on the cylinders, followed by a thorough scrubdown with HOT water and Tide to get all the hone grit removed, followed by a pressure wash with 180 degree or hotter water. A properly-cleaned cylinder will begin to surface rust within seconds of the final rinse water drying away. Apply a generous coat of 30 weight oil to the cylinders to prevent rusting until you can assemble the engine. Good luck!
Jerry
