I know I am a bit late to the update so here is a request if there is a 1.3 update. Can you add the superspeedway rear end? I just think that would look so incredibly good, and would add to the detail factor of this mod.
This will likely not be added to this version of the gen 6, it will be included in our eventual remaster however!
It probably failed because of the difference between tracks and maybe the cars. Try attempting it at Paperclip Park, while the mod is a little broken (maybe even more broken in 0.26) it's the closest we have to Martinsville.
i set the cars to the manual AI setting on the AI Manager in the UI maps, and put in on the "wp10" script and sent them from there. works pretty well too