HERE ARE 6 SIX USED CAST 401 BUICK +0.30 OVER. PISTONS MEASURE 4.2175 ENGINE WAS REBUILT WAS ABLE TO GET 2000 MILES THEN DROPPED A VALVE CRACKED THE BLOCK. LOST TWO PISTONS. I HAVE BEEN HOLDING ON TO THIS PARTIAL SET FOR ABOUT 6 YEARS NOW. LAST PICTURE SHOWS A NUMBER CASTED IN THE SIDE NEXT TO THE PIN HOLE OF 686P. HOPE SOME CAN USE THEM. QUESTIONS PLEASE ASK.