400 HP is not gonna go into a yard kart, or a race kart for that matter. You would be simply building a small car/buggy..... No go kart parts will work with that much power. The most you need on a typical yard kart is like 10.... On a race kart, I see them running upwards of 20+.... But its still a go kart/ small industrial engine....
The weight of a small block and that power level would rip apart a go kart of any type....
You'd be pushing it with 20 hp. 400 will rip apart any clutch, torque converter, tires, or frame you put into it. You would be better off building a car or dune buggy. Something like that. It's far too much horsepower.
400 is way to much, for a yard kart, race kart even a buggy nothing will handle that much, the power to weight ratio will be enough to destroy some of the fastest supercars of it were possible or sane to put on a go kart, my go Kart is pushing 24hp and that's a ton around here