Thanks dvn and TeeJay!
This one is a stainless steel Day-Date using a caliber 1556, gen dial, hands, crown/tube, bezel, DJ case, crystal, 78360, etc.
Many people think that these don't exist in gen form, but there are in fact a small handfull out there. Supposedly, these were gifted to the top students finishing Rolex's watchmaker's program. The cases are without reference and serial and there are variations out there using 1555, 1556 and 3055 caliber movements. The other speculation is that these steel cases were for in-house testing and as such were never intended for public consumption. Whatever the truth, the few that have turned up for sale have traded hands for ridiculous amounts of money. If you query 'Steel Day-Date' at some of the usual gen forums, you'll find that these have been discussed from time to time
A few more pics...
And I've got the parts to do another... Just waiting on new day and date discs along with a couple of other small parts...