Glad you posted to remind me to come back here...
If you do go the jackshaft route and try a kit, do NOT use the bearings they come with. They are absolute trash and when I ran the numbers and compared online they are freaking wheel barrow bearings not even meant for motorized use.
I tried them out and they have a dramatic amount of excessive bearing play under load - as soon as I started giving it gas from a ~15mph roll the bike got a nasty clunking vibration and snapped the short crank chain since the jackshaft actually moves forward ~1/8" due to bearing play which brings the sprockets out of alignment. Added a half link thinking it was just too tight and tested with final drive chain disconnected so I can free rev it and it did the same thing - you can see the movement that causes the sprocket teeth to hit the side plate of the chain, which snapped a link. Even though I was only going like 10mph when it happened it was still very unsettling.
I am replacing them with proper sealed flanged bearings and supporting them with ~1" of a bearing race tube on each side, with a ~1/2" hold drilled in each tube so I can still use inner lock collars instead of just outer. Only ~$20 extra for priceless amount of piece of mind.