Hey i went to my machine shop today and there building a buick v6 short block . The block is a prestage block it has an sp on one side ita 4.1 wit on oil pick up 14 bolts cast cap with aftermarket splayed 4 bolt program caps in the center yea it offcenter the casting number is 4x15198 i was just curious cause its an oddball sounds like one of the smokey yunick deals .