Rather than lowering the SCR via a thicker head gasket, may I suggest another route:

go for tight squish.

Tight squish is when the piston to cylinder head clearance [at TDC] is less than 40 thou Ύ.040in]. Getting that clearance under 40 thou acts to raise the detonation threshhold...reduce the tendency to detonate.

measure the piston deck height on your motor. The older redblocks tended to have negative piston deck heights...the pistons top out below the block deck.

If the pistons are within 10 thou Ύ.010in], i.e., they come up to within 10 thou of the block deck, then you could order a Cometic MLS head gasket of the appropriate thickness, in the case of negative ten thou deck height a HG that is 27 thou Ύ.027in] thick, and get the squish clearance right around 37 thou Ύ.037in].

Depending on what the actual piston deck height is in your motor, you might need a different thickness HG than 27 thou. Cometic offers them for the B20s in several thicknesses.

I realize that this is contrary to what many think. I build Volvo turbo redblocks [SOHCs] that run SCRs over 9.4:1 and 10 PSI of boost...on 87 octane. Tight squish makes that possible.

Besides 'tight squish' as a research term, you would also want to use 'quench' as a search term.

good luck

TF