Unfortunately, I'm at a disadvantage to give you any more detailed information as I'm three people removed from the owner of this engine. I'm a machinist given the task of reboring the block on a vehicle I've never seen. From what I can gather, the Diesel is a three-cylinder so we can rule that out. This is a v-twin gas motor. The pistons I've been provided (Kawi part# 13029-2105) are concave on the top and are 76.5 mm in diameter.
thanks,
Rob