The porting scenario is pretty much the same for a racing boat engine and a competition chainsaw engine.

Typical mods are .020" squish with most probably a widened squish band in the combustion chamber to get the combustion chamber smaller which also involves cutting the cylinder base down.

The relative positions of the upper intake transfers, exhaust port, & piston skirt width are all plotted to widen the exhaust port and direct the intake transfers towards the back of the piston. The transfers are smoothed and timing of the intake, exhaust, and piston port timing (where applicable) are adjusted for optimum flow compromise. Minimum case volume is always a consideration.

Finger boost ports are usually added to the piston ported engines.

Have seen closed port engines have the cylinder way cut away to convert them to open port.

Single thin ring.