Need trans for small diesel

You could build a double slipper belt design. A TSC store or Princess auto or something like that will have all keyed shafting, pulleys and support bearings for what is needed. A single lever attached to a pair of cables controlling tensioner pulleys would work. Straight forward on the stick engages forward and back engages reverse. There are a lot of pulley choices for your 1" keyed shaft motor. Go Kevlar on the belts they will last much longer. Nice thing is very easy to build and down time is minimal seeing how everything is easily replaced.

 

Actually now with more thought my last idea would be a pain it would need a gear assembly or a twisted belt to do reverse could still work though