Colvin's Chevy by the numbers book shows the Engine casting number application as a 1969 (mid year) 427 for Passenger,Corvette,Chevelle and Camaro.Also 1970 and 1971 454 applications.
The heads as 1969 - Passenger/427, Chevelle/396, Camaro/396, Corvette/427, and Chevy II / 396.
The casting date and pad stamp will help narrow it down.
Billy