Jeez...
nope.. with 20" wheels and just a centrifugal clutch that thing won't move at all at a 7:1 ratio
it's a heavy two seater (assuming at least 215kg with one passenger)
gearing higher than 15:1 won't cut it! ( so we're talking 150 teeth ABSOLUTE MINIMUM)
the cent clutch will certainly NOT work at all (that sprocket would be ~ 24" in diameter
)
So you need a Torque converter (series 30 6" driven will do fine)
then the 7:1 will almost be possible (if you stick with one person only and stay below 450 lbs!)
if you crack the 650 lbs in total weight (two adults seated)
you will need 8:1 at the very least still (even with the tc)
and another tooth for every ten lbs above that
(750 lbs 9:1, 800 lbs 9.5:1... and so on and so forth)
anything less and you will just burn out clutches / belts like crazy and won't move much at all.. especially not up the slightest incline.
'sid