Here is a good clip that goes in depth on the differences of 4-stroke parallel twin cylinder engine variations.
https://youtu.be/a9ZFZABaLbg
For 1500 and1800 rpm direct drive generator applications I feel a 360° variant is still the best. The rpm is low enough that primary and secondary balance is not much of an issue.
Too bad Kubota and other small diesel manufacturers do not make a 360° variant specifically for driving 4-pole direct drive generators.
The differences in parts would be: crank, camshaft, flywheel, counter balanced front pulley and possibly a different crankcase breather.
I feel a 360° parallel inline would address some of the harmonic issues associated with a 180° variant running at lower speeds.
Years ago many engine manufacturers made 360° even firing parallel twins for generator applications. Wisconsin had the 360° even firing THD parallel twin. And, it was used on many 1800 rpm direct drive generators. That is one nice running engine.
Henry
I have a friend who has one of those 4 cylinder wisconsin's direct driving 20kw generator head at 1800 rpm. Sounds real nice. Got it thru some sort of surplus with almost no hours on it. like brand new. Wants to sell it. would let it go cheap. Just throwing it out there.
where is your friend located?
i have a friend that is looking for a 4cyl wisconsin to replace a blown one in a skidsteer
not sure which variant he needs, but your friends might work?
bob g