I wouldn't discount the 69' 350 HO. They were the sleepers, usually steel rims with poverty caps, flat hoods, but came off the line better than the 400's.

The 455 with 15's is a nice pump gas set-up, the 350 HO motor in stock form has a high static CR for today.... Hence why the 455's are becoming ever more popular - low comp - high hp.

If all you are short from a numbers correct vert is the motor, I would do it, but you will likley want to put in some dished pistons for pump gas... You can port the heads to flow better with a roller cam and make up for some of the loss with the CR.