Central to the story is the inspired discovery, by Rose, in an Egyptian museum, of a stélé, a funerary object similar to a grave stone; except, in this case, one made of wood. Being made of wood was unusual, though fairly common for the region and period it was made. It was more unusual that the reverse was also painted. The stélé was that of a priest of the martial god Mentu, one Ankh-f-n-khonsu from Thebes (the present-day Luxor). It was thought to be of the 26th dynasty but is now variously attributed (the chronology debate being what it is; and the third intermediate period, as its known, being one of turmoil and confusion) to dynasties as early as the 23rd. It had been discovered, very probably, inside Hatshepsut's temple in Deir el Bahari, in the necropolis west of Luxor, in a cache of sarcophagi of priests of Mentu found in 1858. It is very likely that Crowley was informed of this, as he spoke about the stélé to several museum men who would have known, but he never wrote about it; at least not in any publicly-available text.
The sarcophagi of Ankh-f-n-khonsu, and the box-like wooden shrine they would originally have been in, were amongst those items found in that cache by the great pioneering French archaeologist Auguste Mariette, or one of his excavating gangs at least, in 1858, soon after he was given the founding directorship of the Antiquities Service earlier that same year. He had previously been commissioned, in 1854, to found a museum in Boulaq after his sensational discovery of the Serapeum in Memphis. The Mentu priests' sarcophagi were found in one or both of the two small shrines in either side of the temple, having been placed there in ancient times to protect them from thieves. However, the excavation was not formally documented and I have yet to find a record of which it was; if either. The standard catalogue of objects in the museum, from the founding of the Antiquities Service, was the Journal d'Entrée where objects were given an entry number as they were received by the museum; but often items were overlooked and the stélé did not receive one until the 1920's. Meanwhile, it was given a variety of other catalogue numbers. Despite the common belief, based on Crowley's account, it was not item 666 in the original Boulaq museum catalogue. It did not, so far as I have been able to ascertain, receive this number until the collection was moved to Gizeh.
It was, however, recorded (at least on the card numbered 666, which to this day accompanies the stélé in the Egyptian Museum, in its display case) that the stélé was from Gournah. That was the village at the entrance of the Deir el Bahari valley (since relocated away from the necropolis) so it is clear it was, at least, found in that district. It is likely that the mummy of Ankh-f-n-khonsu was still in the sarcophagus when it was discovered but was unwrapped and dumped there in the valley of Deir el Bahari. Immediate disposal of the mummy, after searching it for valuables, was standard practice in those rough-and-ready early days of Egyptian archaeology. There was originally, presumably, a tomb of Ankh-f-n-khonsu in the necropolis. Others of priests of the period have survived but his has not. The 1858 cache was the first of several found in Deir el Bahari, one in particular much more famous; but also including another one of priests of Mentu, excavated, thankfully, after archaeology had developed into a science.