Hmmmm...I think it depends on what it is that you want them to look like in the end result.
If it was my project I would probably go with the best, darkest sumatras I could find and then breed in some black large fowl Old English Game, or some other similar single combed bird. The Sumatra would give the dark skin and and a bit of game influence, and the OEG would contribute the single comb which is what the cemani seem to have. I believe from the little I've read about them the 'silkie' type feathering is more due to inbreeding and poor feather quality than actual silkie type feathers. I would try to stay away from anything that had white earlobes as that would be very hard to breed out. You would also want to keep hard feather type, so I would stay away from silkie influence for that reason...not to mention the multiple toes and feathered legs.
This would definitely be an interesting project.
Just my thoughts.