i have been thinkin of building one my self for quite a while
firstly it needs to have 2 wheels on the front and 1 on the rear
so i think mounting something like the rear off an apprilla rs50 or yamaha tzr50 or something similar with the engine still mounted to the bike and then extending the built in gear shifter to a hand built short shifter ( something like what they have in some rally cars so you push to go up a gear and pull to go down a gear)
for the front i would suggest something small and agile like the old style mini (any model/company)
the engine should be highly tuned with these parts
tzr50)
-
http://adrenalin-pedstop.co.uk/p/POLINI-RACE-CLUTCH-KIT-FOR-MIN-2683.aspx
-http://adrenalin-pedstop.co.uk/p/ARTEK-KT-MAN-SIZED-VARIABLE-IN-2529.aspx
-http://adrenalin-pedstop.co.uk/p/YAMAHA-TZR-50-MBK-X-POWER-DOPP-863.aspx
well thats my personal idea and what i may build soon if i do i will post pics