KZ1 would be fine. I don’t think they would walk away with times by any means and I’d like to see that question answered. A lot of it will depend on the track’s layout as well. Consider that in the 90’s 100cc karts lapped pretty damn close to open FC gearbox karts on tight tracks. Take that 100cc, add power while keeping weight near enough the same (very doable) and you’re right on the money.
I think that’s what will make it interesting. There’s all kinds of interesting karts out there too. Like CR250’s, with the gearbox cut off, running methanol, dual 135cc C-Open karts from the 70’s with 70-90HP on tap and so on.
So let’s see how they actually stack up, rather than guessing. Build some interesting stuff, have some fun and see what happens. Twins vs singles. New vs old. Light vs heavy. Shifter vs single gear etc etc.