1966 GTO 421??

[Bobcat]

In 1966 the vin was not stamped into the block. The block number was a unit number that would only be on the paper work. Numbers matching was not an issue at the factory. The date codes are within an exceptable span with most purists. If you look your engine over the heads are not nessarily the same date and time and rarely is the head the same as the block date. The assemblers aren't going to take the time to check date codes or casting #'s. '66 Cars may have
one 092 head and one 093. What than? Tell me would you have noticed? I doubt it. If you had an early or late car you got a hadge podge of parts. They used whatever was in the bin and fit was used.