[cjshaker]

It's strictly my opinion, but when dealing with compression ratios, you're throwing darts unless you actually CC the heads and block area. These engines are old, and who knows how many times, or how much, the block and heads have been surfaced. If your iron heads have been shaved a couple of times over its lifespan, it's entirely possible that you could be dropping compression by moving to another set of heads. At a minimum, your iron heads should be CC'd to figure out where they stand, then you can make a more informed choice. Or you could simply have your heads shaved to up the compression (cheaper than new heads), but careful measurements must be taken to make sure there won't be an issue with piston/valve to head interference, or that you're not getting into 'detonation' territory.