I told you the welding blanket would work
Simplest solutions are always best...copiously coat the inside with anti-spatter. After a few cuts with an internal sleeve, it will be covered with spatter and be a pain to remove and insert.
You're going to have to mount your torch with the amount of bevel you are seeking. The nose of the torch will be between 30-45* above horizontal for what you want to achieve.
I would suggest some kind of backing plate between your workpiece and the front of your 4th axis chuck, as this bevel cut will blow slag towards it...don't want that crap on the jaw screws!