Quadricycle style vehicle would be a neat project. I would not recommend a copy of Henry's quadricycle engine though, it had major faults (cooling for one, ignition for another) and would not pull the skin off a rice pudding. I had the start of a similar style vehicle a thousand years ago when I was 18, using a V-4 Wisconsin conveyor belt engine and 2 sets of wheels off 750 Suzuki motorcycles whose engines and frames met an early demise racing. Wheels / brakes still in fine shape. Frames were carefully selected scrap 3" steel channel, rusty and badly pitted, heaven knows how old. The idea was something like Henry's 999 race car I had seen at Greenfield Village Museum near Detroit a few years earlier. My old Dad saw me mocking the thing up on the hoist at his garage one day and just said "no, you are not doing that!"
May have saved my life – it would have gone like the proverbial bat out of hell……..
Little did he know of my exploits with small engine powered bikes, then full race bikes……