73-87 steel bed in a 1963?

[63GMC305e]

Although my GMC is a 1963, I thought I'd try posting in this 73-87 forum for your knowledge in this matter...?
My standard fleetside (swb) bed is trashed- wood and metal bits all a-tangle.
I would like to weld in a steel bed. The 73-87 steel beds are still available in pristine newness. I was wondering how different the short-beds are, in the wheel-well dimensions? The longbeds seem VERY close, but I haven't been able to find a shortbed 73-87 in a local junkyard anywhere so I can measure it.

Anyone able to measure the distance from the front bed panel, to the front and rear wheel well edges at the floor, in a shortbed 73-87? Or from the tailgate edge? Thanks!