Hipo chevy dealers did do something similar to Mr Norm, putting 427s in cars you couldn't get them in..... until GM came up with the COPO (Central Office Production Order). Then, if you knew how, and had a cooperative dealer, the factory would put your 427 camaro together. The dealers didn't have to do it anymore. A COPO order was how you could get a ZL1 in a camaro (but not a chevelle or nova)
I had a friend (since passed) that had a COPO 375 horse 396 camaro.
Why a camaro that could be had with a 396 anywhere, was a COPO, was never properly explained.