I don't think the panel trucks had inside spares, I think they had their spare mounted under the rear floor just like the Suburban. I like your idea of using the second middle seat and mounting it to the right and allowing room on the left to mount the tire. Take some measurements of the space that is left after you mount the rear seat. If my memory serves me, it's 14- 15" Maybe a side carrier found on the pick-up can be mounted on the inside left panel. It might be a close call.
Another thing to remember it's cold, it's dark and your parked on the side of the road. Do you want to take out the rear seat to get to your tire?
What about a suit case style tire carrier mounted under the rear seat? This way you can still store things on top of it in a pinch (There's not much room left anyway after the third seat is installed)
Back to one of my earlier ideas, finding a space saver wheel and mounting it either on the left side of the seat or underneath the seat with an upholstered cover? Do They make space saver wheels in 6 lug?
