:doh: sorry, should have read that bit about being a 3 door!
Are the seat runners a good 4 or 5 inches in from the side of the seat and the tilt base about 12 inches wide? If so then it's only early disco seats to replace the existing with.
You can fabricate a plate that bolts to the existing base that you can then virtually bolt any seat to but you'll need to watch you don't restrict the lever for tilting the seat.