Yes, there was an 18K Camaro - the reference number in the usual place between the bottom lugs should read 7228. There should also be an assay mark stamped in a blank plate above it. It should be a 3-register dial with the Valjoux 72 movement. They're pretty rare.

For everyone, there's a helpful hint in the model references for a while around the end of the 60s and through a large part of the 70s. It's not a hard and fast rule by any means but it might help if you're on the spot and faced with something unfamiliar:

Reference ends 3 - case is stainless steel

Reference ends 5 - case is 20-micron gold-plated. Caseback is steel

Reference ends 8 - case is 18K gold. Caseback is also 18K gold

It's a loose rule, granted, but if it helps someone make the right decision or better yet avoid the wrong decision, then I hope it's worth pointing out! Earlier solid gold Heuers also used 14K gold but by the time this numbering convention was in place, they should all be 18K.

Mark