Wow, your a real DIYer. That really is cool.
Having 0 experience with using the bike gears, I dug around a bit. This link gives exact ratios; http://motorbicycling.com/showthread.php?t=32814
Which is 16:1 and only 24 MPH but a jumping off point, any way. (His rear sprocket is a 30T. dunno what yours is)
I searched with the words shift kit to make part shopping and basic concept similar. This is what came up; http://www.google.com/cse?cx=partner...kit&gsc.page=1
But some one will join in and help, I'm sure.