you could use either of the 2
3.5" 1929 A GA =25 (long range aa)
or
5.1" 1932 A dual GA= 34 (short-medium range with strong aa power)

the four big t slot, i think it was suppose to be mounted by 5.1" 1932 A quads in combination with the 5.1" 1932  A dual but now i know why they didn't allow it, its kinda AA OP ship since it can fire its aa at all direction... so just mount all slot with the aa guns you have choosen

just try both first on what aa guns your good at...