I reconstructed the cockpit seats and instrument panels because they were Airfix/Italeri-style just flat panels. Also I added seatbelts on the front seats, and completely rebuild the passenger seats using fabric for the rear areas.
I had an M60 laying around from my Tamiya HMMWV, and built an ammo box for the final touch on the interior. I used an old IDE hard disk cable for the ammo belt.