Comment on Dreadnought by thefirstfleet
I think it is possible. I don't know if it was a deliberate design feature or mere coincidence, but there is something that looks like a separation line on the big gun, just where the saucer separates. How the gun is being able to fire without the Warp reactor... that's another question...
Perhaps there's a secondary reactor in the Saucer similar to how the Prometheus class has separate reactors for each section.
WHat I have in mind is a fusion furnace that powers the gun. And only the gun. It's part of the kit, not originating in the Galaxy's original configuration.