My '62 Suburban came with two sets of seat mount recesses in the floor: One that fits the narrower 2nd row seat, and one that fits the wide 3rd row seat, allowing me to but a wide seat in the second seat position, and no seat in the very back, so I've got 6-place seating and cargo area.
The guy I bought the truck from had a '60 with the same set-up, but he never realized it and sold me the third row frame for $100 when I bought the truck. Two minutes after I explained to him what I was going to do, he wanted to buy the frame back. Bwahahahaha!
My Suburban also has solid, 1-pc windows in the 3rd position, sliders only in the middle row.
Maybe some of you guys with a third row seat, that only want two rows, and simply move the mounts. A router would make short work of cutting the recesses.
Brad