Dragon
Hi and welcome. I sold my 1924 built log cabin on Yellow River by the youth camp in `91 and moved to Fl. Are you 72? my Uncle Matt Cameric had the bar in Cadott for yrs.
Your trike would be easy to motorize. If it were mine, I would think about driving the left rear wheel. the axle would need to be a little longer in the center for a Staton sprocket adapter and lock the wheel to the axle. Your pedal power would drive the right side and the engine would drive the left side, left side on pavement more than the right side.
It appears that you have room for a large axle sprocket, as you don`t want a lot of speed with a trike. It was easy for me to put a friction drive on one of my trikes, but the frame is different.
Stay in touch, you will get lots of help.
Ron________ PS; Just re read your post, 2 seater ? I thought it was a weird scary unstable feeling when I rode it by my "own-self" . L8R