The timing chains and OHC's, getting the cam timing correct. These blocks can only be over bored .020, but I'd doubt that you would even need to bore it anyway. If it is indeed a rod knocking, I would just put a crank kit in it and be done with it. These engines last a very long time usually. If you do rebuild the whole thing, get good valve guide seals, the early 90's engines were bad about them leaking and burning a little oil..