Best way to reduce compression ratio?

You can blend the chambers a bit, if you're saavy on a carbide bit (round and cone do well, combined).

Lowering compression does help with detonation. Ultimately, changing valve timing, combustion temp, getting good quench and lowering overall cylinder pressure will help.

Aluminum heads help, because they have better heat/ quench properties.

Inkjunkie's suggestion is a good one, too. Retarding the cam or running a camshaft with more overlap will lose it.

Running colder fuel can help (ice box, air gap intake, rerouting fuel lines away from the engine, electric pump, resin bodied carbs drop temp about 20F, etc.)

Retarding the cam's advance cycle can lower compression, because the intake valve closes after the piston is already on it's way up.

I wouldn't suggest retarding ignition timing, as that can cause more heat issues.

All of this is going to cost power, but it can save your engine.

Water injection may allow you to keep the power you have and use it at WOT or under pinging conditions.

If it were me, I'd get another set of heads, keep the quench, go with the same gaskets and dial the cam in nice with a good chain.