TENERGY has a battery that will fit. It's charging!
A YouTube video shows a mod to fit the 4200xl battery. It's a bit more than I'd want to do.
https://www.youtube.com/watch?v=sBnKbfavp94
The video also goes through the radio controls. They're what you would expect. The only question I really had was how to shift low/high.
My questions are answered, at least for now.
A1 Dirt