Evan
The MC on my '51 just has a single line attached to it and uses two division blocks over on the right side of the frame, one splitting front to back and another splitting to RF and LF. The one you're referring to is used on only some AD's (52 and later?) I think I may have seen them somewhere, which would be easier that machining your own. Have you looked
HERE?I think you could cut the seat with a tool ground small enough to cut the seat and the undercut on a lathe, feeding it in parallel to the seat angle, either before or after the threads are cut.
