There's quite a few variables.

Rule of thumb for a cold water engine (one that typically runs open loop water and temperatures rarely get above about 130°F at WOT) you will add .002" to. 004" to the piston skirt to cylinder wall.

The cylinder wall finish and ring type (and end gap) all come into play here.

NOS, blowers,  turbos, and fuel type can come into play here as well.

For example,  alcohols runs much cooler than race fuel as far as cylinder temperatures.

A good machinist familiar with building marine engines should be able to point you in the right direction.

Just know that the factory spec for a motor home engine will not fly.

Good on you for asking the question,  if your machinist does not ask you questions about what the motor is going in,  you have the wrong machinist.

Good hunting.

GT



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Awesome thanks GT, basically I'm trying to budget build if at all possible. My plan was to find some small dome forged pistons that'll work in closed chambered heads, and hone my cylinders if at all possible.

Just don't forget that the balance of the rotating assembly will be effected with different pistons.

I always recommend have the block honed on a CK10 or similar. It ensures cylinder symmetry and consistency. Shouldn't cost a lot.

JMHO