A pair of huge beams up top can do anything, a large corrosive multicannon below is good for added damage effect (if needed just pull up the chin give it a quick blast to get the effect otherwise ignore it) and the other slots are for whatever you fancy just for laughs as you don't really need them. Force shell cannon is hilarious.
Oddly enough, that's exactly my loadout.
I'd suggest a pair of pulse-laser turrets in the medium slots.
Give 'em a G5 long-range mod' and they're superb for "tagging" everything in a CZ to maximise your CBs.
Also give 'em the "Emmisive" XFX and they'll prevent a lot of ships blinking off your scanner when they pop an SCB - as many, many NPCs tend to do.
*EDIT*
Regarding the C3 hardpoint, I have
no idea how it manages it but my C3 multicannon has pretty-much the same arc-of-fire as my C4 lasers.
Presumably, it makes use of the same witchcraft that allows the FdL's C4 weapon to fire upwards, through the hull of the ship. [where is it]