I think most of the econoline seats from the base up, are the same bolt pattern. The earlier bases, like my 96, have a slightly different bolt pattern where the base meets the floor (I'm not sure where the cutoff is).
I just did a low budget seat swap for my van last summer. I picked up a passenger side base from Ray (1Der on the forum) and a new set of leather 'take outs' from a Honda Odessey van, middle passenger seats, from a couple guys that are always at the Goodguys show swap meets in Pleasanton ($300/pr I think). But the Japanese seat tracks are a different width than Ford, and I had to do a fair amount of fabricating (cut, grind, drill and weld to fit, paint to match) to make them look and work like factory. They turned out nice, but it took me 8hrs per side.
The seats I took out, are aftermarket van conversion seats w/armrests, the type you see in 1990's motorhomes and conversion vans, blue crushed velvet. Those tracks adapted pretty well to the Ford bases.
The seats I took out are available in exchange for a 6 pack of beer