IIRC 67-69 and 80's LA rollers (which have the 302 head) are advertised as 9.2:1.
That's about perfect for pump gas 87 even.
No need to change pistons unless they're junk.
In case no one's mentioned it, you'll also need to address the K frame/engine mount issue, and some other minor bracket and cable stuff.
...and let's not forget gross vs net HP.