Maybe it's time to take a step back and think about the project as a whole. Ask what your grandpa and others around you think. From my point of view, with the amount of rust damage to the substructure and the amount of welding, fabricating, or finding replacement metal and the time and cost involved, I question if it's worth saving. I wouldn't waste the time and effort in cleaning stuff like the carpet that is probably already stinky from the mice and worn down to the point where there is no carpet. It might be better to remove the entire interior as well as the gas tank and spray everything with a soapy bleach mixture. If you're still trying to save it, start with the metal work first, but reassess as you go.