identify the year of my 360 long block

Yep, that helps. Year depends on if that is an "Oh" at the beginning or a "zero", could be a 1978 or 1980 360 HP.

Honestly, I wouldn't worry about the HP specs, there wasn't much to them and if it has been rebuilt most of the stuff probably got changed. In 1978 HP didn't mean much more performance anyway.