Neat find.
Take off the high hoop on the seat, the goofy paddle extensions on the pedals, the plastic bucket seat and maybe even the engine and it looks like a early 60's race kart. It has a Simplex Challenger flavor or vibe to it with that short steering shaft and the rectangular pedals, but has a wide-hoop steering brace (I believe that is an early kart feature) and I don’t see many wide-hoop Challengers in ads/photos/brochures.
There’s a few other karts that look like Simplex karts but I don’t remember what brands those are.
Good Honda engine on there, essentially the 'cream of the crop' of industrial engines.
I’d hate to steer you away from our fine forum, but ask the same question at a vintage or rear engine kart forum and see what they say.