Just had a better idea- - - -I remembered I've got a few Mercruiser 4-cylinder inboard/outboard engines stashed away, the same basic engine that was used in the 4-cylinder Chevy II back in the early 1960's. They have the same bellhousing bolt pattern as a small block V8, and/or a 230/250/292 6 cylinder.
That would simplify the installation of the basic engine/transmission assembly, maybe a Turbo 350? Then I could add a short 3-speed like one of the torque tube transmissions I've got sitting around, and couple that up to the 2-speed rear axle. Gears galore!
Jerry