If we're just talking about a ship that's a big set of cargo canister racks (volume 2m^3 per canister) with a few engines and thrusters around the outside then it could carry 200,000t of cargo in that physical cuboid space. The larger ships have so much internal volume spare on paper that even a box the size of a Type-6 could hold several thousand tonnes of cargo.
Obviously the catch there would be that it couldn't move because the maximum mass on 8A thrusters is only 5040t (and the thrusters themselves take 160t of that, then add on fuel, hull, other core internals, etc.). With the requirement for it to be able to move at all with 8E thrusters, a ship with a total normal [1] mass over 3360t is probably not possible.
[1] You can with ridiculous choice of engineering blueprints make a Cutter which exceeds the maximum mass of 8E and 8D thrusters (though I think you can't quite exceed the maximum for 8D while the 8D are fitted to the ship) but that is very definitely not normal.