I don't think there's a chance of holding together my composure! Will have to laugh into my armpit. Wood kart with...........nails? Seat belt (lap belt) via trousers belt? Ape tape? Balsa wood? 100 mph plastic wheels? Wowwwwwwww! I'll call you Daddy if you'll put me in your will.
Every bit of that except wood and 670 makes no sense.
If you can build a vintage Morgan spruce-frame replicar with that motor in it, go for it. That means not one single nail, screws only. Balsa wood on aesthetic parts only, no structural. If "monokote" is the laminated honeycombed aviation grade Balsa and marine plywood used in the DeHavilland Mosquito, the Spruce Goose, etc. then you could make it structural using vertical axis only. No seat belt at all, not even as a lapbelt, if you're not going to build a crashworthy rollcage, you'll need to be thrown clear in a rollover before it snaps your neck. Inside of a rollcage, a lapbelt's not enough, need to restrain the torso too, think harness. Canvas-skin stunt planes have had a lot of highly specialized tape used on them, but aerosurfaces aren't structural, that's all done by internal ribs. Plastic wheels are truly flat-free, don't even need innertubes. Just a garbage bag to pick up the pieces when it explodes at any serious speed. Rims, hubs, spokes, intestines, femurs, eyeballs, etc..................Daddy.