Seems like it's geared for about 20mph. assumming 9K at the motor and a 10" tire. I came up with a 13.8:1 ratio without your maybe sprockets if I read it right.
Personally I would at least support the rear of the engine or put a gusset ot 2 in the motor mount. And I don't know about the clutch it's probably a little light for the application without a lot more ratio or a varaible trans, looks like a fun project.
Might look into something like this:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=290219663298
Or this:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=250337233246
Both have a clutch bell built in.
Jeff