With a little motivation and a welder, almost any seat can be made to fit.
For a van, I find armrests on the seat to be particularly important, since most vans don't have a tall center console. Astro/Safari/Express/Savanna seats might fit the bill. VW Vanagon and Eurovan seats are SUPER comfy and have great armrests, but the older Vanagon seats may be harder to deal with aesthetically unless you recover. I believe there are some Land Rover seats with arm rests?
Your best bet is to just keep an eye on junkyards and grab the first set of clean seats that looks good and meets your needs, then worry about "fit" later. Having a local welder build up a custom base or slider adapter should be cheaper than shipping seats.