Chevrolet script valve covers? I'm not sure what you mean by magneto font, but I have a set of Chevrolet script valve covers that came off an early 283 or maybe even 265.
Instead of the bolt holes being straight across from each other, the top two are closer together than the lower two. If yours are the same it means you have some very early heads, which would not be original on a 305 or on any other small block made after... I'm not sure exactly when, but late '50s or early '60s.
I'm thinking those were not used any longer when the 327 came out in 1962, but my memory is vague on some of these details, and they could have stopped even earlier, like maybe 1958 when side mounting became standard.
You may need to check all the casting numbers to figure out exactly what this thing is...
