I agree with Jim? on this one. Giving it TD and Precise would be a bit too much, especially with that stat-line. Very few races get TD, P weapons, even EA with their significantly more advanced Marathon Advanced Cruisers and Warlock Advanced Destroyers don't get anything of the sort.
I personally don't like the trend of interceptor-ignoring weapons, particularly with the dearth of beam weapons that now ignore hull 6, both of which combine to effectively remove the two primary defenses for all EA Ships (High Interceptor and Hull Values being rather useless against beams, and these proposed Mag Guns), especially since there is no evidence as to the limitations of WHAT a Interceptor can block, merely HOW much (A key reference for which being that; In Severed Dreams, where the XO to Major Ryan mentions that they can use their aft beam batteries now that the Clarkstown's interceptor grid is down). However, I think the stats that Jim? came up with for the Mag Guns, as is, are pretty balanced. I like them, and I'm the one who ends up fighting the Narn, not the other way around.
As for the G'quan and its variants, I would either go for:
1) As Hiffano said, make their beams Forward Arc, and keep their AD as is. (Though, I would argue, various EA ships should get forward arc beams as well, notably the Omega).
2) 6 AD Beam, but still boresighted.
In addition, Battle and War level Narn ships, at the minimum, should have 10 inch secondaries, not 8 inch, as previously established.
My gaming group also created a house ruling where the G'vrahn has its AJE dropped to a JE, loses its Command trait, and its E-mine is One-shot instead of Slow-Loading. In exchange, the Bin'Tak gets Command +2, and its E-mine becomes Slow-Loading instead of One-Shot.