Need a width measurement-flat bed

[trapperjack]

found a factory flat bed for my 67 long bed. not sure what year it's from, oak floor, metal frame and divider strips. I need to know how wide a flat bed should be for a single rear wheel truck. I'd measure the truck, but it's not here yet. I don't want it too wide, and not sure how wide a single rear wheel bed would be vs a dual rear wheel.
Doesn't have to be a factory set up, just trying to get an idea of if i want this thing. I have to replace the bed on the 67 when it gets here anyway.
thanks in advance.
trapperjack