He may be able to get by with ah definitely looks like a homemade Manco 400, just out of square tubing. But yeah wow out of all the homemade ones that one looks pretty dang good! Change out those tires though.
Small note - Looks like you won't be able to fit much else other than a flathead on there given how close the seat is to the engine plate. So if you wannt to run something like a Predator (which I think would look wacky on that neat vintage homemade frame), you'd have to either move the seat forward or the plate back and reweld it.