[njsteve]

The 7H1 cylinder head was used on the 1972 350/160 and 175 horsepower 2bbl engine. Valves are 1.96/1.66 resulting in 7.6 to 1 compression ratio.
The "YW" stamping looks kind of weird like there is something stamped under the "W".

Verify the numbers/dates in my above photos and post them. We can then tell you what it is/was.

You never go by just the cylinder heads since Pontiac fans tend to swap heads to make different compression ratio combinations (like what we are doing with Gramma's car - adding the 96 CC 1975 6X-4 heads from the ultra low 7 to 1 compression 1975 350 to a 455 block will give you a 9.5 to 1 ratio 455.