Thank you for posting more information. The ANSI Buttress thread form has not changed since it's beginning that I'm aware of. Just very minor things that would not affect form, fit, or function. So it should not matter on which MH you use. I would suggest hand grinding a threading tool since the thread is not being mated to another thread in this case. It's just being used as an "easy out" type of thread for extracting a seal as you have mentioned.
I hope you have a taper attachment that will handle that steep of an angle. I think as long as it has some sort of taper to the thread, it should work. Sounds like a cool project to tackle. I don't have any threading tools ground up for a Buttress thread that fine of a pitch. I have some Top Notch inserts that I believe are ground with a 45 deg angle on one side and 0 deg or perpendicular on the other that may work. It would require a top notch holder to hold the insert.
As I said, I believe your best bet is to grind a tool. Let us know how you make out on cutting the thread.
Ken