Chevy/Mercruiser Question

[Capt. Chad]

My friend is in the process of trying to hook up the new used motors in his 1970 31'. He pulled out the original 427s and dropped in a pair of 1991 502 Mercruisers. Does anyone know if there is any adapter that will just let him "plug and play" the wire harnesses? I havent seen them yet, but he said the new motor harnesses have 1 extra pin and he wants to avoid cutting off the connectors and hard wiring if possible. Does anyone have any advice? Thanks!