I would like to know if it is possible to build a relatively simple 3 speed helical transmission. I am building a motorized bicycle to resemble a classic motorcycle, and a 3 speed gearbox would really help with the look and also make climbing hills a lot easier. The pto shaft is 5/8" counter clockwise. My current gearing is 13.58:1, d like to have that for a second gear, and have a first gear of around 15:1 and a third gear of around 11.5:1. I would also like to keep my automatic clutch if possible, and use a jockey lever for shifting. Can anyone tell me if this is possible, or if there is already a 3 speed gearbox that will fit a 5/8 counterclockwise shaft? Thank you.