Ok a couple of things...if the seat isn't broken down from hundreds of thousands of miles, the OregonAire cushion that turtle recommended IS WORTH THE INVESTMENT...it works.....before id buy a seat, idbuy one 1st..even if you still end up with a new seat, the cushion is still a great investment.
as for a Van conversion seat...they are NOT the best of quality as far as the closed cell form they use..it will break down over time...mine lasted about 2 yrs....as far as the mounts, seats are made to fit anything and have multiple slots and holes for the mounts to attach to the base of the seat and then the van base...every factory seat i have replaced (3) i have taken the mounts from the old seat off and installed them on the new seat making sure they were in the proper spot on the seat so they matched up with the base in the truck. also make sure that you adjust the length of the "seat adjustment (back and forth) cable, its no fun to do after the seat is in...
So with all of that, Id still buy the Oregon Aire cushion 1st.....you wont regret it.....