Here in CA they were called Custom Cab's, as with the Trailblazer and Trekker more than one company did the conversion.

Basically they just stretched the frame and added extra seating.

You really can't get that much appreciation for their length from the photo, but they are about 3' longer than the standard cab/bed.

It is going to take some work to restore, there looks to be radiator support/radiator/inner fender damage, likely bent frame right behind the drivers tire, I imagine the front of the engine may be damaged as well. It is all fixable, just wont be a quick fix.

Depending the price, and your plans it could be a nice to platform to rebuild.