It will all depend on how tall you are, what seats you buy, and if you auctually want the seat to move or not???
If you are tall above 6FT there is nearly no way you can get a bucket seat that fixes from the bottom ( nearly all steel construction bucket seats) and have enough room to fit a mounting rail.(without lowering the floor).. For my first sprinter i bought Cobra Clubman seats, and had to be fixed as when runners were fitted it lifts the seat too high.
If you buy a Fiberglass or carbon eg Sparco Pro2000 which is what i run in the rally car, they mount on the side and can be adjusted by unbolting it from the L brackets and moving it to a different hole forward or backwards.
Someone out there might have different experiences???