Stamped 4/71? Where is that stamped? There are 3 numbers to look for on a 340, the CASTING number and 2 STAMPED in numbers. The first stamped number is on the face of the block just below the drivers head/deck surface, up to 1971 should look something like "GW3403345XXXXX" etc. later years had different stampings in this location. Then the VIN stamping on the machined pad on the lower passenger side of the block just above the oil pan rail. The casting date is a month/day/year on the side of the block.