[JWL]

Radical porting can be avoided with a supercharger and head design/revisions are much more important than any block relief.

Even with the block or heads "O"-Ringed there will be a limit to the CR (compression ratio) the engine can withstand. This lends itself to making desirable combustion chamber modifications.

I never saw any power improvements with dual plugs but never tried them with boost pressure. I think the plugs should be in the transfer area, clear of the valves, and biased to the exhaust side.

The Bonneville rules do not allow modern computer ignition systems in the Vintage Engine classes.