You most likely have "346" heads. They're ok for a mild build for the street. How deep in the hold are the pistons? Those engines had 9 to 1 compression, advertised. In reality less than that.

I have a 383 out of a '71 Newport. Pistons are 0.020 in the hole. I milled the heads 0.30, blended and ported the heads and had a 3 angle valve job done. Installed the heads with steel shim gaskets. Running the Hughes Whiplash cam with headers and a 750 Holley. Runs pretty good for what it is.

The Whiplash cam is designed for engines such as yours with stock exhaust manifolds and intake. Hughes