Geoff Stenner
Hello,Colin. If, as you said, the tender wheels aren’t insulated, you’ll need to get one side at least insulated; both sides might be better as , if not, the tender body will be live to one rail.
If the loco WAS three rail, the driving wheels and bogie wheels may also be uninsulated both sides, so you’ll need to arrange the same thing as the tender. Possibly a brand new set of wheels all round to go with the new cassis might be a thought; spoiling the ship for a ‘happorth of tar comes to mind.
Only thing else I can think of is to try the chassis frames against the body and make any required mods. early on.
Hope that helps, and good luck with the project.