Definitely doable.
You need a rear hinge as stated, maybe a front latch, a fuel pump/filter, a tank cap holder or bung, and most important is an external fuel pressure regulator.
Any injected steel tank will work.
We have a thread...
http://www.ducatimonsterforum.org/index.php?topic=541.0 It might be helpful.
The only other consideration is the seat cutout. You said you weren't concerned about fueling. If you're making a switch to carbs, any tank will work '00 up. The earlier tanks had a different relief for the seat. A seat swap, and any tank will fit the frame with a hinge and possibly a front latch.