Briggs 420

I posted this in the open/limited forum, just more curious than anything, but I love these big 4 strokes.

Has anyone messed with building one of these engines? They are 3.54''x2.6''=419.4cc much like the 420 clones. I haven't seen anything about these so I don't know if there any racing parts available, just seems like a neat engine. It is a Professional Series Snow 2100 on Briggs website.
I have mine apart and have started the experiment.
I'll keep you posted on how the patient turns out.
While I've always enjoyed twisting the snot out of small engines, at heart I've always believed in the old hot rodder's maxim, "There's no substitute for cubic inches". I can't wait to see how this one develops!
Looks like a gx390 on the outside. Looks like gx390 header and intake fits. Valve cover and fan shroud inter chang. Hope to be able to get a billet rod and good piston.
I have a predator 420cc from Harbor Freight. The parts I mentioned before are predator parts not gx390 parts
Since it is a clone I think think the Honda parts fit. Never had a Honda only clones. Just don't want to mislead anyone.
Raced it a couple of times now runs good and makes good power. Has Racseng flywheel and rockers. Parsons rod and piston. Not sure who's cam is in it. Either Parsons or Dyno.
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Torque monsters with lower revs? How hard are y'all twisting them? Spins tires at will or tamed with carby and clutch settings?
Ohio Valley Karting Association(sprint) has had a light (400lb) and heavy(450lb?) classes for a couple of years. Both classes have 6-8 karts each.