Sorry, that was a typo, they are from a 71 car (71 Challenger in this case) SPD was September 18, 1970 so obviously castings dated August of 1970 would not have gone onto a 70 model year car since 70 production was over with by then.

Quote:

Some early 1971 340 e-bodies have been known to have the 49-53(last 2 digits of the casting numbers) castings as the 1970 models.




I have never seen a (proven) original 71 model year E-body with 1970 manifolds, do you know of a documented exception?