Forget battleship mounts on destroyers. . .they put battleship guns into tanks. (Well, perhaps cruiser sized guns)
Mobile artilliary pieces "Self Propelled Howitzers" are heavy guns on a tank chasis.
http://en.wikipedia.org/wiki/Image:M110-203-mm-howitzer-yuma-1975.jpg
A 203mm (8 inch) gun on just enough vehicle to move it around. . .essentially for this vehicle, the mount, the engine, the fuel tank, and the crew positions take up all available weight and cubage. (Ammo carried by an auxilliary truck that followed this unit around.)
That's a cruiser's main gun mounted on a vehicle that is essentially smaller than the weapon itself.
As long as you can fit everything you need into the space, no reason you can't have a wee vehicle carrying one giant spinal weapon or something similar. . . .of course, the example mobile gun is barely armored. . .I'd bet it offers protection to nothing more than frags or light small arms. . .
By this logic, non hyper capable craft could use the space and tonnage normally given over to the engine needed for H-travel to a big gun. . .they'd be the equivalent of the gun-boats of napoleonic times. . . .a rowed or stepped mast vessel that had one front pointing fixed gun, that tended to be really large for the size of the vessel. . .totally un-seaworthy, used only for close in port patrolling.
Or, for a more modern example. . .a boomer sub. . .a WWII aircraft carrier sized submarine that is essentially an engine, crew quarters, life support and a giant honeycomb of cells, each one of which contains a single shot ICBM. . .something like 70-80% of the entire submarine is just tubes filled with missiles.
But stuff like that. . .the mobile gun keeps away from danger, the gun boats used the coast or port for cover, and the submarine is a stealth weapon. . .
If you pack giant weapons into a small hull, the balance factor seems to be the "Sledgehammer mounted on an eggshell" problem. . .a boomer sub has loads of punch, but if it's a target, it will not actually take much punishment.