Hi there, your plans sound good, I have the same truck and have also used a wooden platform bolted to the tank surround. Seats are 60-40 split bench from a Ford Ranger from late 80s, fits like a glove and seat back flip forward to access the space back of seat. I swapped out the under seat tank for a later Chev truck one attached to passenger side frame rail. However I later put back the stock tank, leaving the filler neck which I had to flatten a bit so the seat fit nicely on the wooden platform. Today there must be an unlimited amount of seats that would fit.
Best of luck
Also, take a look at my pics and check out this Ford seat, has served me well.
Check out this underseat storage set up that Deve has done.
http://devestechnet.com/Home/SeatDrawers
