For a EB you need the rigidity to keep the body from sagging in the center.(the doors won't fit) The one Broncitis has is a little diff. than mine but would do the same thing. His has 2 beams for support and mine uses 1. We used a 2x6 1/4 wall beam and made each of the 8 body mount supports 3 way adjustable.
If you use a frame be sure it is square and level, they never are. If you want to get the body off the frame add 8 blocks
That larger single beam is a pretty cool idea for even more access to work areas and the extra adjustability of the width and height of the body mounts would give it more flexibly for other applications.
I agree, you need a rigid structure to support these bodies, and also need door braces and bed braces.
Simply attaching to the front floor and tailgate mounts with arms off the rotisserie is asking for trouble IMO. Some of those other pics also look to have a lot of flex in the support frame under them.
Bronco tubs without proper support under them and without door braces with taco right where the bed section meets the seat floor pan behind the rockers.