Are you the same guy that was over on MB.net? And are you the same one who has the frozen J-arms? If so, I'm the same DMoneyAllstar that was advising you to sell it and buy something more complete. ;) You need steering wheel/stem, seat, axle, tires, cage, clutch, brakes, skid-plates, drive-train, fenders...which is like 85% of the buggy and 90% of the cost.
I've done a Yamaha 340-twin swap on an FL250. It was a fun intro to buggies and ran awesome, although it sure was fugly. There are pics of it on my MB.net profile. It took a total of one sled and two partial FL250's to complete, plus a roll racing cage I found on CL.
But some advice...
> Honda doesn't keep this stuff around, so the 2nd-hand market is your only source
> Build a make-shift base for your
Engine and make sure it runs before you go spending time & $'s on stuff
> Decent fab skills and basic tool set are a must (welder, metabo, wire wheel, etc)
> Your best bet for drive-train for your 340 is the stock FL250 axle, pillow block, e-brake, and CVT gearbox.
> Stock rear brake caliper may be pricey to find in good working condition
> Spend a lot of time fitting the Engine in the rear as LOW as possible in the chassis
> Make sure you have room for the sled exhaust pipe, as there isn't much real-estate behind the seat
> Make sure you have the clutches aligned perfectly AND that both clutches accept the same width belt. Plenty of choices out there for belth length, but they don't make one in two widths! ha
> If you have the sled primary clutch and it works out, the stall RPM may not be right where you want it.
> If you use a racing seat or seat from a car...note they don't offer much clearance for your legs under the steering wheel.
> Use a YFZ350 Banshee radiator -- they're a dime a dozen.
> I'd get the Engine & drive-train installed and running before going crazy on an elaborate cage.
> If using the stock steering wheel with throttle, you will need a custom throttle cable made.
> Repair any rust cancer on the parts you do have.
Good luck with it, and be sure to post pics!