The block is a 1978-85 350 c.i.

You're right, the crank appears to be a GM forged crank.

The heads appear to be 1975-76 305 c.i. 62cc 1.72" intake/1.5" exh.

The heads appear to have been installed to boost the compression ratio, but they aren't going to flow enough to support that 270H cam or a 268 cam for that matter. I'd change the heads to something that would flow more volume if you are planning to use that cam.