Maginot Line might not be the best comparison as this one sounds more like a true castle.
Really? When I think of a Star League Castle I am thinking of NORAD or Cheyenne Mountain rather than a defensive line like the Maginot Line here or like Tamar City during the Clan invasion. I think a Castle is beyond what the FWL could do here in ten years since the Andurien War even though defenses may have existed before this. Perhaps it is just two different visions.
I could certainly see a Heavy Turret (AC/20) or two being present to deal big damage. I was also thinking of massed AC/5 batteries as they have good reach and deal solid damage. AC/2s are too light for anti-Mech defenses but would make good anti-aircraft fire.
This brings up a good topic though which is counter battery fire. I am sure MAC has artillery just ready to open up on fixed positions not to mention aerospace support which I will have to review.
Marcus Barton in his Devastator will likely be leading the way in this assault.