What's under the stamped steel black cover on the very end of the transmission? (right side of this photo, above the transmission mount - click to zoom).
I think it might be the 5th gear set. But I'm not sure.
Reason I ask: might there be something in there that could be an attachment point for an electric motor? (I'm always thinking about DIY hybridization of the gas Firefly.)
Best case scenario: underneath there is the "other" end of the input shaft, and somehow you could mate a cog to it which could then be belt- or chain-driven by an electric motor (holding the clutch in, to keep from spinning the ICE).