Cordelia says that Angel is 248; he corrects her to 247. This indicates that Angel is counting from the day he was sired (and not including the hundred years spent in Acathla's Hell dimension), in 1753 (he was already 26 years old at the time).
When Angelus tells Darla his plan to turn Drusilla, even she seems appalled. It's a testament to just how twisted Angelus really was when his evil deeds made other evil things cringe.
The flashback scenes take place in England in 1860.
Kate sends a police SWAT team to search the Hyperion Hotel. In real life the Ambassador Hotel which substituted for the Hyperion was used as a training ground for police SWAT team exercises.
The conversation Wesley and Cordelia have about Cordelia's visions (and how they affect Wesley's salary) mirrors one between Cordelia and Doyle at the end of I Fall to Pieces (1999).