Vintage go kart with a snowmobile engine

That sounds pretty wicked! I don't think I would personally go 70 MPH on a kart, but I still would enjoy the power :D
Seriously though........I wouldn't let my kids drive it. The one I built had a cage (flimsy one but still). The cage won't keep your arms and legs or head from getting out during a roll over. Even with a seat belt your arms will still get knocked loose and will get broken if you're not careful. Have fun but be safe!!