Only GM engine that used the same block was pontiac. both the Buick and Oldsmobile used a different block for the 350 and the 455. Being this car is going to be given to my best friend who is a not only a 1970 Oldsmobile Rally 350 owner but an Olds enthusiast and the son of a retired oldsmobile executive and will know the difference.
I may look at the 400 in the 69 442 kit but don't know if it was based on the Hurst/Olds or the 442 as the H/O had a 455. ( retro fitted by Hurst)