Had a 413 in my 64 300. Cast, built and stamped as a 63 motor, with the T (for 63) overstamped with a V (for 64).

Original motor? I dunno, remember no VIN stamp back then. But it wasn't an anything special car with a need for numbers matching, I bought it in 88 before all the numbers matching craze hit. My theory is they built more 413's for 63 cars than they needed so they restamped the left overs to put into 64 cars.

It definitely was not a 64 motor, 4 bolt valve covers, rocker arm pedestals. etc.