GMC V6 engine compression ratio

[LSGarage]

I'm a couple of years down the road from this but might as well get some feedback on it. I have a 67 GMC 4WD with a 305E V6, manual trans. Specs say it has 7.75:1 compression.

Question: How much compression can you add to this engine before you run into overheating, head gasket sealing, valve clash and other problems?

I'm thinking of taking it up to 8 or 8.5:1 when I do the engine. But I would like to know how high you can go before these issues begin to surface. I'm looking increase the torque. Maybe a low and flat torque curve. No revs over about 4,500. Maybe going to the Holley 2bbl on the stock manifold, headers, duel exhaust and all that stuff. Its got 3.73 gears in it now but I think I want to go back to the original 3.54 or there about ratio. And I running 31x10.50 tires.