Timo, are you thinking of two turntables on the flight deck or the below deck hangar? If you stop the forward bulkhead of the flight deck at just aft of the nacelles that is really really tight. If you extend it out like I did, you could put two turntables on the flight deck. But as I mentioned before, all the footage that is out there now wouldn't work without some editing as none of the shots are tight enough to crop out any of the structures. (And I've experimented quite a bit with my virtual set.) Or alternatively, a wall is raised between the two turntables which would explain the blank wall behind the shuttle in JTB and TIS.
But that also adds some complication - how does the shuttle move from one turntable to the other? And how does it fit with what we've seen?
BTW - Mytran - neat composite picture!