I saw a RAV4 EV that had a trailer with another battery pack on it. I don't recall if it could disconnect for shorter trips or not. It appears he is putting a camping trailer on top of it. Not sure of the Spark towing capacity but an interesting idea. https://www.youtube.com/watch?v=s9eU_GkOIbc
Some of the Gen 2 Volts had a faulty switch in the shifter that had the same symptoms and required replacement. Someone tracked down the actual switch part number and showed how to replace it. Chevy actually changed the TSB from changing the shifter assembly to just plugging in some sort of bypass w...
Have you tried craigslist or ebay motors? I've sold a car on craigslist and know a few that have sold their cars on ebay. One even sold their car to someone in Europe, they paid for someone to come get it and handle it getting shipped to them.
I'm unaware of anyone on here that has done anything as far as a conversion. I did see Richrebuilds did some work on a Spark EV and has a video of some of the work. https://www.youtube.com/watch?v=1HeEK5cLNpw