[mr48chev]

I had to do some hunting on this one Still didn't find the usual info but a 250 is a 1 ton and it looks like the one ton came as a pickup with the 8 lug rims like the 3/4 tons had, the big truck rims front and rear with single wheels on the rear or the dual wheel version. http://www.oldgmctrucks.com/page0010.html

I'd think you are going to find out that your granddad swapped axles when he changed the truck around to be a wood hauler.

Cool truck with a real family history. I think I would do like you are planning and build a new bed while shortening the frame back to it's original stock length. A nice 8 or 9 foot flatbed would look real good with some stake racks that weren't too tall.