Manta could actually use a 2-2.5k armor reduction.. maybe even 3k to balance it out.. and maybe lose the torpedo mount on it as a trade to keep it's current agility...
So all in all:
reduce armor 2k
remove torpedo mount
leave agility as is.
RP:
The Manta is essentially a Hammerhead fighter, but with slightly better firepower sporting 4 class 10 weapons and 2 class 9 guns aswell as an improved class 10 shield. Unfortunately however, this fighter loses it's torpedo mount and the magazine space designated for those torpedos.
EDIT: Side note, on that gunboat turret (I nearly crapped my pants when I saw that) I can't wait till Igiss rebalances the rest of the cap ship turrets to be equivelents. At first I thought he was full of crap because my corsair turrets still do the same damage. lol
(Yes I said Corsair turrets on my BHG BS.. they are sold on Rostock with the ship, so RP Is not violated here)