Here's another option. I have a 1969 318 block-heads- rotating assembly in the corner. That should have the higher CR. Should I just build that with either the 340/360 heads or a pair of 302 heads?
302s would be your cheapest bet. Although you would make up the price in porting them to get decent flow. I spent 20+ hours on mine to get them to flow decent. If you get a set of say 596 heads with a chamber of around 69-72cc, get them cut .025 and end up with a nice 64-66cc that would net you a compression of around 9.0-9.5:1. Just a suggestion and option! Correct me if I missed something