Surprisingly there isn't a great deal of commonality on the weapons load outs for the Excelsior class. There are a number of different "cannon" style examples available on the web, but nothing consistent. This ship is bigger than the Constitution Heavy Cruiser and contained five banks of 2 phaser emitters each on both the dorsal and ventral sections of the saucer. Apart from that, variations abound.
Some examples have both forward and rear facing photons. Other examples do not have the rear facing photons. Still other examples have turret mounted phaser emitters on the engineering (main) hull of the ship. The phasers for the Excelsior are listed as Type 8 but for the Constitution class as being Type 5 emitters. So, in the end, I have gone for a compromise.
I have listed both the rear photons, the central turret mounted phasers, and rear mounted phasers seen on some "cannon" examples. All phasers are Phaser I's. This makes this ship a beast of a vessel compared to vessels of The Original Series. But one would expect improvements in power distribution systems and firepower over the intervening years. Moreover, during Star Trek The Undiscovered Country, the Excelsior was seen as a big vessel compared to the Enterprise and would have been the Battleship of Star Fleet in its day. By the time of The Next Generation, the Excelsior class was regarded as a workhorse all rounder and a Heavy Cruiser. That's how I have viewed it here for ACTA. Basically its a class of ship that depending on what era you play ACTA, this ship can be either the battleship of the fleet, or a heavy cruiser. Anyway...Boldly Go and all!