heres what we came up with for gears on a friction drive. the roller is a 3 speed hub with the center nurlled. this is a project we work on when ever we have extra time so it's not done yet, but looks promising.
http://motorbicycling.com/attachments/f26/16633d1259534073-acme-lowrider-lowrider3.jpg
What is this engine? that is a really neat looking hancrank ideal for the engine.