I have zero experience in flying or outfitting battleships. That being said, based upon what you told me about the Arbiter's weapon spread before, it's unlikely that you'll hit a snub craft with standard weapons.
A flak or two would help throw off the predictable wave of nova bombers that will delight in your sheer size. My first question is this: What is the most common ship class you encounter on the Arbiter? Being a heavy battleship, it's definitely got the core to support a double Heavy Mortar loadout, if you want to roll the dice. Alternatively, you could stick with Hellbores for sustained heavy dps against large targets. Being that the Arbiter probably wants to be up close and personal, I wouldn't recommend Nightmares.
Not really sure about the rest of it. I'm probably the last guy to ask for help on this, but the flaks I feel are a definite must, if nova bombers are a frequent concern.
Signature is SEVERELY out-of-date, sooo I'mma figure out what-do with it later!
You'll have problems deshielding those little, dodgy Liberty dreadnoughts, so take 4 pulses. Mount 4 hellbores as anti-hull armament. You can also go with 2 hellbores and 2 mortars or heavy mortars, but only if you can aim the latter well. Both of these armaments are good for fighting cruisers, too, and usable against gunboats. As of the rest, 2 flaks (used for deflecting/detonating torps/missiles; make sure they have 360° coverage) and rest secondary cannons would be alright. Not sure of the ship's secondary arcs, so I don't know if secondary coverage is strong enough to make solarises effective.