Sounds like you have enough room in the rear for some nice custom designed ported cabs. Those dimensions are almost identical to the jtr cap. 1400. A little tight for huge ported cabs, but being rear subs nearfield, not as much would be expected of them. A couple UM’s or similar back there in the corners would be great. Like my nearfields are small, but because they are nearfield I don’t have issues with port chuffing or anything with a 2” slot port. I guess I’m saying that’s what I would do. You could even keep the Cyclopes all where they are currently. You have 3 behind your screen, one in the rear, centered?