Theres only about six inches behind the seat as I raised the backend to get them closer to the bulkhead and achive more leg room as I have the old floor mounted pedal setup, I have twin extinguishers tanks so I dont know if the angled tank would fit behind the seats,I would doubt it though.
some of the others may know better.
As for the fit they are really snug but they are really comfortable the gear lever is a bit of a stretch for first but still havent modified the lever yet, might just shorten the rods instead as the new seating position is lower and further back compared to the last seats the lever no longer fouls my leg in 3rd and 4th and there are no clearance issues with the handbrake.
you could possibly go for a wider seat yet as I just wanted as narrow as possible for playing around with the angles for a better position.
hope this is some help jamie
