That is not a complete1960 Manx Norton anyway, and it may not even be 500cc. 1959 and later Manx engines had the “Lighthouse” cam drive, the cam drive surrounded by the engines fins and an AMC gearbox, not the laydown box this bike has. Typically 350 Manx Nortons ran the reverse megga and teh 500cc jobs had a straight megga. This looks like an early 50s oldham coupling engine that someone has stuck into a mid-50s or later frame with a late 50s or early 60s front fork.
That is not a complete1960 Manx Norton anyway, and it may not even be 500cc. 1959 and later Manx engines had the “Lighthouse” cam drive, the cam drive surrounded by the engines fins and an AMC gearbox, not the laydown box this bike has. Typically 350 Manx Nortons ran the reverse megga and teh 500cc jobs had a straight megga. This looks like an early 50s oldham coupling engine that someone has stuck into a mid-50s or later frame with a late 50s or early 60s front fork.