I worked on one of those for a mate of mine. I think the first 5TAs arrived in 1960. The 5T finished in 1959, and would have had the distributor where the magneto was on the pre-unit Triumphs. My 500cc Triton was made out of 650 bits, but with a 63mm stroke billet crank. The crank in the unit 500s was 65mm stroke. But the only ones which had a proper bearing in the timing side, came in 1973. I saw a complete bike at a swap meet for $2500. The motor would have been eligible for pre-63 historic racing, but it would have involved making gears. The Percy Tate 500cc Triumph which beat the MV500 at Spa was a development of that motor. My 500cc short stroke Triton could beat any other 500cc four stroke racer. It badly needed 6 gears. Any four stroke engined bike which can beat a 1962 Manx is good.