We're working on several parts of the truck at the same time, or trying to.  My body guy is finishing up the smoothing of the firewall.  I'm about to start getting the frame ready for touchup paint (fixing my blunders and uh-oohs) and while he'd doing his thing I want to fit up the bed wood and start on the finish procedure for the wood.  I probably could have done it with the bed sitting on the floor but old knees and hips resist working on the floor and will complain greatly when forced to do it.   So I fabbed up a dolly to hold the bed at a decent working level and at the same time keep it square and plumb so I can mark the holes for drilling.

I made it long enough to hold the bed and the rails are the same width as the actual frame width. ( 34" outside/outside)  It's built from 2.5"x1/8" square tubing with three cross braces and it sits about 26" high over the cast iron wheel dolly casters. It rolls with the touch of a hand. I chose that height why ?? Because I had a short of material that when cut in four pieces came out to that height !  Didn't have to wrestle with a full 20' stick...  that stuff is heavy and I'm old !

Once the bed was in position I centered it up on the dolly and attached the tailgate and hinges.  Then I made sure it was  square and plumb, pulling diagonal distances across the bed and using levels to get the sides in position.  Actually closing the tailgate got it nearly perfectly plumb and I wiggled it a little and got it square within 1/8".  Then I clamped it to the dolly in four places  to hold that shape.

Now the bed wood fitting can commence knowing the bed is square and is at a comfortable working level.