Jack shaft with 2 bearings and 2 gears. You can mount the jack shaft high or low or forward to avoid the gears hitting the cross frame or more slick would be to have the jack shaft slide over the lateral frame member with roller bearings inside. The right side chain stay would need to bolt on (not welded) so you can install the jack shaft and it's two gears.
Offset wheels make for some really bad handling. I rode one like that. I had to lean as far to one side as I could just to go straight and turning the opposite direction was impossible.