Tremec Magnum six speed bellhousing issue

Sorry to say, but you are out of luck, all of the modern Challengers with the 6 spd Tremec have the starter on the right side of the engine, passengers side over here, drivers side over in your neck of the woods.
The automatic cars had them on the left side.
Like you said, you will have the look and see which aftermarket company makes a bell for a left side factory small starter.