As far as the brackets you could make them one of two ways you can relocate the seat farther back on the seat tracks or move the entire seat assembly farther back by making brackets.
Relocating the seat on the tracks you would start by removing the seat from the floor and then there will be 4 bolts or studs that hold the seats to the seat tracks and you would remove those and then you would fabricate some plates that would be rectangular in shape and you would drill 2 holes maybe a couple inches apart and then you would bolt the brackets to the seat tracks and the other end of each bracket facing rearward and then you would mount the seats to the 4 rear holes and reinstall the seats. I would only move the seat back the least amount required.
You could drill additional holes on the seat mount end to try different adjustments
Now for moving the entire seat rearward if the studs on the floor mounts are long enough to accommodate an additional 1/4" for the plate then you could add plates there to move the seat rearward the same procedure would apply for making the plates with the only difference being you would want to drill and tap the rear hole and run a grade 8 bolt from underneath and this would serve as the new mounting studs for the feet.
I also feel the GTO seat could make you problem worse since they are larger and have heavy bolstering.