A heads up on these bases - These are designed as direct bolt in, no mod required units for the 1997 and up E Series. The 1996 and and earlier vans have quite different seat mountings compared to the 1997 and newer rigs.
Seat Belts - The seat belt attachment latch on the 1997 and newer is integrated in to seat, the 1996 is attached to the floor.
Seat Mount points - The 1996 seat track bolt patterns are different.
Floor bolt Pattern - It is different and modding these to fit requires drilling holes in the floor unit and shifting the seat base unit to fit and still swivel.
If you are changing your seats to 1997 and newer you will have addressed the seat belt and seat mount issues. The floor bolt holes will still need to be drilled to adapt or new holes will have to be drilled in the van floor for bolting with new backing plates.
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com