I am new to this site, so sorry for the late response. Here is a link to a cart that had a 2005 R1 motor installed in it and I believe he used a rear axle from a Honda 250R Quad.
Personally, I wouldn't use that big or that high of a performance engine. It's way overkill. 12.2secs in the quarter mile is a death trap, (carts have poor stearing, high center of gravity and 111hp @ the wheels is like having a honda civic with 1000hp, its useless. No traction or control.)
A 400 to 600cc 4 stroke street bike would be more realistic. If geared properly would still have plenty of enough power. Or a 250 to 500cc 2cycle if your going to be really running it "not a trail rig, 2cycle don't like to be idled or ran slow, plugs faul."
I am considering the same project, just remember, you will have gears to make up for brute power. Everyone running the 24hp v-twins only have one gear and a large slow engaging clutch. Not that that is a bad set up. I just think (just speculating) that and 80cc 4 stroke off of a small 4 wheeler with an auto clutch and gear shifter (stock set up for an older Yamaha 80cc childs wheeler) would be able to preform as well if not better than a v-twin 24hp Honda engine. The cons would be having to shift gears, motor would have to be turned on unlike the gas and go set up for a normal cart. Some larger Honda 4 track model 4 wheelers "late 80's had a built in reverse" I think the125 and 200cc had it.
Anyways, look around. There are a lot of other options that can be more economical. Sure an R1 is a sick motor, but not in my opinion ideal.
Hope this helped, Even if it was long winded.
