As I said, the B18D (8.7:1 CR) that's the stock motor for a 122S runs just fine on 87-octane, using the R+M/2 standard. The B18B (10:1 CR) is the 1800S / 123GT motor, and it much prefers 91-octane or better.

I am very much against using thick head gaskets. Efficient combustion requires that the piston comes close to the combustion chambers, and the stock design is already far from optimum in that regard. The thicker gasket not only reduces CR, it *requires* more timing advance -- there is no gain to be had from it; it's all negative for performance, economy, head/valve temperatures, and pinging.