Someone should design a modular mission module to slide into a Hercules to make it a gunship. If side doors were added in the right places a pallet could be made the size of the cargo bay with heavy guns and ammo stores mounted. Any Hercules with the doors added could load the module and become a gunship relatively quickly and when not needed it could be used for humanitarian and cargo missions. It would not likely be able to mount guns a large as a dedicated AC-130 carries but should be able to mount guns large enough to make a potent gunship for close air support. You could even add some AGM's and rockets to wing hardpoints if weight allows.
There are multiple iterations of this idea already, including the AC-130 Specter Gunship, kits that allow the USMC to attach Hellfire ATGM's to underwing stations of a C-130 and even a pallet allowing you to fire small "Griffon" missiles from the ramp while in flight.
Of course, the shootdown of an AC-130 over Kuwait in the 1991 Persian Gulf War during a daylight mission demonstrated that the gunship isn't viable in contested or defended airspace, and to my knowledge, no daylight missions have been undertaken since then. Even at night, there are insurgent forces which have MANPADS and the ability to use NVG's or other devices which would make operations difficult for a cargo plane, much less one flying low and slow for an attack run, and against a modern near peer enemy, you would be toast. Russian Spetsnaz
operators with MANPADs essentially cleared the skies of Ukrainian SU-25's in the Donbass, and the SU-25's are analogues of the A-10. If a dedicated ground attack aircraft isn't going to cut it, then adapting a cargo plane won't work very well either.
The one thing a C-130 could do in the modern environment is serve as a "mothership" for UAV or UCAV's, an idea the Americans are exploring now. This is far different from a gunship mission, however.