454 was never offered in the Chevelle by the factory until 1970. The Biggest they put in the '67-'69 was the 396. Some of the Dealers did swaps and offered them with a 427, but very few were done, there were actually more Nova's that had the 427 installed by Dealers. 427 engines last year was '69, and in '70 they came out with the 454.
Owned both a '68 & '69 Chevelle SS's with 396's. Much preferred the '69 as it was first year with Disc Brakes on the front and stopped much better than the '68.