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Not sure on the caravan seat, but most "new" seats end up coming from an 80's Ford Ranger. The wheels are a standard 5x5 1/2" bolt pattern that includes IH, most older Jeeps (before they went to 5x4 1/2"), most Dodge pickups (except the late 70's when they went to a smaller bp too), and of course Fords before 1997. Wheel backspacing/offset may be different though.
I used the flat springs from Caravan and "fitted" those to my original bench frame. If I remember correctly, the middle and back seats of Caravan were too short and too long respectively. I have a couple pictures of the seat frame in my gallery under cab mods, I think.