AV-MP- is interesting. "MP" meant maximum performance on the 63 and 64 max wedges. The "A" could be for 1965. The "V" could be for 1964. Someone may have stamped it twice. I have found left over 426 max wedge parts put into production late 1964 and 1965 cars. I once found a 1964 426 wedge marked "A42" meaning 426 street wedge. Took it apart, it had a 1/2" factory swinging oil pickup, 426 max wedge rods and crank. The rest was street wedge and this engine was never apart. Get the casting number off the block. that will show if it is 413 or 426 block. I see it has an AFB on it.