I think it would more work than its worth.
And the newer GM van mirrors are really any different.
I would suggest doing what U-haul does.... Ditch the GM mirrors, and go with Velvac. THey are not extendable, but they are available in several arm lengths and can be heated and lighted. The U-haul 10' box vans have short arm, since the body is not any wider than a regular van.
(they show a widebody model in the pic, but if you check out a small U-haul you can see what the 86" model looks like.)