By the time you spent the money building a Industrial engine you could buy a Honda or Yamaha V twin and have 1.5 the HP. I think it would be cool to have some big thumpers instead of 17k RPM screamers.jmo
Might as well run the 35, touch more stroke
Dyno cams can grind a mean cam for one
Performance v twin makes rods, push rods, and roller rockers
They also make a billet flywheel, but you have to swap the ring gear for a steel one off a factory.
You have to do away with case gasket or it will leak within a few hours and case will crack( machine end play into it and yams bond)
Put arais flat tops with long rod and deck heads .010" or stay stock piston/ stock rod and deck .050" or shave stock piston .082" and run long rod and deck .020"
Manley makes 6mm valves for that engine.
Put a Mikuni 42 hsr and let er rip.
FYI the valve seats are bad about sinking in that engine
Or you could run it stock....... But that's no fun
If you want a V twin, my vote would be to stick closer to the roots of micro sprints and choose from the rice burner entries into the V twin market established by Harley; there are plenty of choices and wrecking yard packages aren't any more expensive that their rice rocket counterparts. The old "small engine" Honda Shadow (700cc or 750cc, can' remember exactly) would be an easy setup.
Actually, my choice would be S&S Cycle's reproduction of a late 1930s knucklehead Harley engine, but that would set you back approximately what it cost me to acquire a used 600 micro and race it for the first season...
I've been thinking kind of a long this same line, been kicking around the idea of a Kawasaki KFX 400 or a Suzuki Z400. I know in places they have run a 450 on them so I don't think the 400 would be that big of a reach. The 400s have in that 30-32HP range but will be water cooled and are made 4 stroke.
back in 2002-2004ish Chuck Kidwell was working on using some sort of similar engine as a replacement for the 600cc crotch rocket motors. I actually saw one car with one on it racing with the 600s at one of the indoor concrete/coke syrup "rumble" races in Indiana or Ohio and it seemed fairly well matched on a super tight track like that. I can not for the life of me remember if it was a Briggs, Honda, kohler or what it was but I am pretty darn sure it was a twin cylinder motor. He would be the guy to get in touch with if you wanted to pick his brain. Last I knew he was in Indiana building Kidwell Jr Sprint chassis.