If you can find a skilled and creative body man with a plasma welder and the courage and skill to figure out how to solve (any) problem, then with a few bucks and 5-6 hours, you can solve this thorny project of moving a third row bench seat to the middle, replacing captain's chairs. The major puzzle - the seats do not share the same base fitment - one that can seem to defy logic.
I found such a guy, a young car builder, who saw a way to make this happen, and in 5 hours, he did it, and did it well (as I think the photos illustrate).
One of the bases each of the captain's chairs was saved, used to mate with the altered base of the bench seat. The bench had a click into tunnel fixture while the captain's chairs were held down at four corners by bolts through the floor. The inner frame of the outboard captain's chair was saved and plasma welded together to form a new base (see photo of the base) and the same approach was made for the inboard base.
Then the bench seat was bolted to the new base and thanks to GMC design, the seat belts were completely useable in the transfer as they remained attached to the van inner side wall.
Even if an OEM middle bench could have been found, the new, redesigned base would have to be built, so there was an advantage, in this project, to use the existing third row bench because 1) the captain's chairs were used a part payment for the job and more importantly, their bases used for the new middle seat base and 2) it was there and in excellent condition and 3), it seemed to be the same width and style a the OEM middle bench.
In my case, my "builder/artist" brought a bonus. He took extra care to make the job look sort of like an OEM conversion. You can be the judge of that - I was more than pleased with the look.
The "new" seat is comfy, is solidly attached to the floor and will withstand a crash event, looks decent in place, allows movement back to the cavern (back space), matches the interior, and provides full and correct use of the seat belts. Also, the bench retains its adjustability - and is shown now in rearmost position.
Lastly, the wife is VERY happy.
Comments or questions welcome.
Be not afraid. You want middle bench seat? Find an "artist" and grab a few hundred bucks and go 4 it.
"There are two kinds of ships; submarines and targets".