then unless your building the engine (which wouldnt be the most reliable) my advice would be to scrap this idea and get a good used engine that you dont have to piece all together.

It sounds like you want to put the current pistons in your bad block in your new block If so, this will require machining, rings, bearings, gaskets, etc. At this point your well over what it would be to get a used engine from a motor mall or yard.