It sounds like you may have welding experience,so this is just a reminder. If you are needing to remove that much supporting metal, I would weld in cross bracing in critical areas. After that much cutting, getting the door to realign corectly will be very agravating otherwise. Tack diaganol bracing across the cab WITH the door closed, then remove the door to finish the welds. Then add the door frame bracing. Cut cabs without bracing tend to torque.

Drew