If he got chased by the cops he could say a lawn mower was chasing him!
The design does have an advantage that it could be removed to power other stuff (Generator, power tools*cougH* compressor, etc.)
Here's some links that I've had for a while in favorites for similar type stuff:
Parts, clutches...
http://www.softdisk.com/sites/gokarts/clutches.htm
Trailer Idea isn't new:
http://www.staton-inc.com/photo_gallery ... PhotoID=48
That link has gear boxes, parts, interesting info. (Motorized wheel barrow gears and parts.)
This link has in parts the rear sprocket. For higher HP motors, maybe it could be mounted on a mag wheel with bolts. However the clutch chain size would have to have compatably spaced links.
http://www.kingsmotorbikes.com/index.html There are many of the 80cc kits for under $200 on ebay I've seen.
There's a bike someone added a jack-shaft and ran the original chain, shifter, and bike gears (claimed over 50mph with 49cc motor because of gear shifting efficiency. I'll try to find a link to that. (I had an idea how to run the gears: Motor to jackshaft to bicycle shifter/gears easily and forgot now DANG!!)
Here's one with lots of parts and a 110 cc motor I'd like to install on a Tomos moped frame sometime:
http://www.fancyscooter.com/category002 ... otors.html
Really I'd like to build something like these one day also:
http://www.vortexplans.com/ OR:
http://www.rqriley.com/tri-mag.html (Gallery of peoples' builds on there) 8)
For your gear ratios I'd say just do the math comparing to what works for go-karts (or application) only scale up the wheel diameter you're using.
I want to check out ant's formula when I have time. It looks cool. 8)
EDIT: This bike pwns it, (Just not for endurance):
http://www.rqriley.com/imagespln/jetbiketest.jpg (That's from the page the tri-mag plans were on).
