You gotta love peoples "car knowledge"

455 would be an Olds motor, Chevy had the 454...I know picky, picky...it still not a Mopar..
Buick and Pontiac had 455s as well. They're all very different creatures, but I favor the Pontiac.

There was a guy at Schucks (Checker/Kragen) who I'd constantly send on a wild goose chase. I'd ask for a chrome differential cover for a Ford 9" rear end about once every 6 months. He'd end up calling other stores, or dig out huge parts books to find it.
You may consider having him run down some hardened C-clips for that 9" if he hasn't gone off the deep end yet.