I have looked into this a bit in Oregon, and here is what I came up with. 3 wheels can be a motorcycle, but 4 wheels is a car. I think there is a clause that states that an ATV can not be made street legal. However, here is the conclusion I came to. If you could convince DMV that you scratch built this "car", grind the vin number off, show a whole bunch of receipts for steel tubing, engine, wheels, etc, then you could possibly register it as a car, just like scratch built street rods. It would need to have a windshield, wiper, seat belt, fenders, turn signals, horn, etc. I really think you could do it and make it look good with fenders that are barely legal. However, if you ask DMV in advance, they're going to say no. If you build it and take it in to register it, there's a chance that they will say, "That's not a car. Get outta here." There have been people in other states that made a swingarm set up for a single rear wheel, registered it as a motorcycle, and then swaped it back to 4 wheels. But, it wouldn't take a very smart cop to figure out that it's not a "motorcycle" anymore.