I've got a question that I need backing on. I think that 76 z's were only equipped with a cat converter on california models, but I cant find any info to back me up. Is this true, and if not, when were they put on as stock?
I researched this topic recently and can confirm your suspicion. Only CA emission models had the catalytic converter. Even though I live in VA, I was forced to keep it up to CA standards because of the emission tag on the hood. Federal (other 49 states) exhaust systems had a resonator in place of the converter, which is a drop-in replacement (size-wise). I found an excellent after market converter at Trak Auto in Northern VA. They even had it in stock! Seems like I paid about $90 for it. Beware of the universal type. They typically require some customization and can be a pain. This drop-in replacement worked very well.
I have a 76 federal version...non-cat. The door sticker says conforms to ferderal usepa standards etc, etc, etc...then at the bottom in all capital letters it says NON-CATALYST. Thats one of the reasons I bought it.
Hope this info helps.