Don't be so fast to reject the Pontiac 455! Get some early valve covers and put GMC decals on them.

Some later 50's GMC's had Pontiac V-8s, and your 455 could be dressed to look like one of those. That would be cool and plenty powerful.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...