what does sonnax list for a rear servo kit ?
i have a superior kit on the shelf for an A518, it's number is K029, while the 904 number is K030.
the od. is 2.810". however, i never got around to using it, so i can't tell you if it fits the A518/727 or not.
i measured an old 727 junk case on the shelf, and it looks really close to 2.810". hard to get really precise because it's so cruddy.
i don't know if this helps you or not.
mr. kunkle would know for sure.