not too hard to build a bottom end mate, granted that theres engine building and then theres building a mighty engine, but if you want a standard engine and you reasonably mechanically minded aslong as rings are gapped correct, in the right order and everything torqed etc should be fine. I personally think if its apart get crank ground if needed, balanced etc as this helps loads, no put putting a crank that needs grinding or something back otherwise engine will never have good oil pressure. anyways if your unsure im gues thats why your looking at learning and seeking help and best of luck to you