You pretty much answered your question in your 1st sentence. "Basically bone stock" would be the main selling point I'd push and the truck still being 6v only adds value to that......
I purchased a 6v battery from NAPA for around $100. You could possibly find a cheaper rebuilt 6v battery at a rebuilders shop. A 12v battery will run the same or more and you'd have to add/update other parts inorder to allow the truck to run on 12v.
re. 6v charging. Unless the reason the truck was parked was because it wouldn't charge, a cleanup of the generators brushes and regulators relay contacts should get it charging again. It'll definitely need polarized which is a very simple and easy step.
A running basically stock AD has higher value than a non-runner but it all depends upon what you want to put in it and how much you want rid of it...
Good luck
Dave
