Looking at the specs, the Light Gauss would be an effective replacement for the AC/10 in many cases. There's an additional 28 damage per ton of ammo over the AC/10, and the extended range bands would help. However, the minimum range would be an issue. For the Enforcer and Orion, the LGR would be a quality upgrade as it improves reach, Centurion and Hatchetman, not as much as in those mechs, I see the AC/10 in a shorter-ranged role.
The important thing is to find the role for all the equipment.
Depends on what you are looking for. In the mass band we have the AC/10, Inner Sphere LB-10X, and LGR.
A straight up AC/10 for LGR swap gives 60% more ammo if the bins are swapped one for one, and a medium range that goes out to beyond the AC/10's long range, and a short range that goes out nearly to the AC/10's medium. Until you get to 5 hexes or less, it is effectively a pulse AC/10. Sure you loose something in the damage per hit, but the ammo capacity per ton is high enough to work out to slightly more damage potential.
Compared to a LB-10X? With two tons of ammo the LB-10X has slightly more shots, and more total damage potential even if carrying a mix of slugs and cluster. OTOH even with the cluster round, the LGR is still has a couple range bands where it is superior in accuracy.
I'd say it comes down to role. A LGR is better for something that wants to hang at range, say a Hawk Moth, or refitting a LGR in place of the AC/10 of the BSW-1X Bushwacker. It would probably work decently with the Centurion, though I'd probably want to remove the rear medium laser for extra LGR ammo there. Two long range weapons with deep bins, it can play the battle cruiser game, beating up more vulnerable targets at the edge of their weapon range, while more comfortably in its own. And able to run from something big enough to get through its lighter armor.
LB-10X is more for the inclose fighter and slugger, roles like the Verfolger, often paired with a ER PPC for either two ten point slugs, or a PPC hit with a Cluster chaser.