Is unleaded OK to use in a 1976 vette?

Use a lead substitute which you can buy at your local car parts store. If your engine has been rebuilt for unleaded then you don't need that stuff. Also use ZDDP in the engine oil.

Removing the lead in the gasoline was a disaster to older engines that needed the led for protection and coating the intake and exhaust valves. When the lead was no longer used, there valves would burn, creating issues with the engine performance and smooth running. Like Js8016 said above, it is not an issue from 1971 and above. In older vehicles, it requires a complete head job to put in parts that can function without the lead additive. Yes because of the higher compression, you need to use as high an octane as you can get at the pumps. A complete tune up, including timing is a necessary also.