I have never heard of the surname McAloch. If it exists it's extremely obscure. As you rightly say, there were/are two gunmakers with the name Malloch. The more famous probably P.D Malloch, himself probably better known as an excellent angler, and for making the finest fishing reels of the time in addition to the gun-making business.
Malloch's is still in business as a gun and tackle dealer, rather than gunmakers. Still a good shop, and well worth a visit if you are in the Fair City.