i am repowering my boat with a 496 and was wondering where this part goes ? part # 863023c

The part # doesn't seem to be the same but I would guess it's # 2 in the link which is part of the water drain system. It would be located on the stbd side of the motor aft of the sea wtr pmp. It's an early model, the later models are part of the actual pmp itself.
http://www.mercruiserparts.com/Show_...R+DRAIN+SYSTEM