They were but corporate rules prohibited anything larger than a 400 cu in engine installed in an intermediate or smaller bodied car as from what I understand they did not want those cars to compete against the Corvette. That obviously changed somewhat with the COPO (limited production) and then again in 1970 with the LS6 and Corvette had nothing anywhere near that Chevelle.

Not to be argumentative, but isn't that what COPO essentially did?

COPO worked with significant numbers of cars/trucks - large orders with dozens or hundreds of vehicles. And/Or with a high-volume dealership that had clout because they themselves sold THOUSANDS of vehicles, e.g., Yenko or Gibb. Hardly one-offs.

If Don Yenko had harnessed the COPO process a little more aggressively in 1966, yeah, I believe he could have made 427 Chevelles happen. But he didn't.

Which is a shame because it would have made for a fantastic car.

You're talking about relatively significant COPO orders, although 50 cars isn't really a lot. COPO was also for more simple requests wasn't it?

edit: I guess it really wasn't. Even still, the 69 COPOs Gibb ordered wasn't really a lot of cars it seems. Definitely not one offs though.
"Instead of placing an order for Camaros using the “Regular Production Option” sheet, used by dealerships for performance and styling upgrades, a dealership began ordering Camaros using the Central Office Purchase Order (hence the name COPO), which was generally reserved for adding alterations to municipal fleets."

https://www.gmpartscenter.net/blog/b...of-copo-camaro

"Experts." I stopped hanging around my cars at shows because of "experts" who would talk you to death if you let them.

I guess Chrysler was different from Chevrolet. They WOULD build anything, specifically Hemi cars. You just had to go to the right dealership (like Grand Spaulding Dodge) or know someone at Chrysler. You read their ordering forms that state that the Hemi was available in certain cars and not available in others. Yet there are Hemi 4 Doors (1966), Hemi Belvederes (1967), Hemi Coronet 440s (1968). They even proudly show a 1969 Hemi Charger which was not available (had to be an R/T) in one of their PR photos. ALL built by Chrysler - no dealer conversions.

Those cars were built in larger numbers, and the COPO was approved to further an agenda within Chevrolet. The COPO 427s were to support backdoor racing activities. A work-around to corporate policy. It was all about promoting brand image at a time in history when drag racing was "hot" in popular culture.

I've never seen any evidence of such a program in 66-67. It would have required substantial effort and cost, and they wouldn't have authorized it just because a person wanted to buy one that way. I would imagine you would have needed solid upper management connections and a 50 car minimum before they'd even consider it.

It's also worth noting that lots of stuff appeared in PR photos that never made it to production.

66 copo
 

I believe the 66 yenko stinger corvairs were copos because of the dual reservoir master cylinder. Please feel free to correct me if I am wrong.

Thanks for all the replies, I did win the argument as he said 66 and 67 Chevelles had 427s which I said they didn't from the factory. 1969 would have been the only time that happened with very few built at the factory as a COPO Chevelle.

Was there an RPO code assigned to Pete Estes's Z/28 convertible?