As far as moving the seats back, you are probably already there. The seat back mounts almost flush with the cockpit rear bulkhead. If you move the seat bottoms rearward, then you gain nothing but less seat bottom. With a butt like mine, that’s a no-no.
Your room will probably come from moving the steering column toward the dash.
Sounds like shortening the “spliced in” part of your steering column is in order. How close is the blinker stalk/wheel to the dashboard. You’ll need to leave knuckle room and room for the blinker stalk.
The plane of the steering wheel should also sit parallel to the plane of the dash board…in other words the same slope/tilt or angle. That’s how the real TD’s are.
Post some pics of the progress too