Best way to reduce compression ratio?

Another suggestion you may want to give a try;

-cooler temp. rated thermostat
-coolant additive that helps transfer in the radiator with new coolant
-colder rated spark plugs with a couple (literally 2) degrees of timing retardation
-shroud your radiator fan (if you don't already have one) go to a direct drive fan, vs. clutch or higher CFM electric. I would recommend an OE fan that fits your radiator dimensions, over an aftermarket. They just work better, from my experiences. Junkyard and a tape measure can do a lot for you.

One thing that I have seen done is reflective coating on pistons and cylinder head chambers. Even if you were to just polish the cylinder heads' chamber cast surface up a bit with a ball sanding stone bit and some sand paper, you can help heat reflection ( which is also one of the reasons aluminum works well) and reduces carbon build up.

You may also consider some seafoam to decarb. O2 sensors, even if you tune and cap it off, are awesome for a lot of reasons.

If you are running headers, you may consider wrapping them. There is a silicone spray that is on the market, that helps with deflecting oil soaking into the wrap, if you have any leaking issues.

Basically, anything you can do to reduce heat is what you are after. Start cheap.