The lines that Dryden recites ("Be judge yourself, I'll bring it to the test: / Which is the basest creature, man or beast? / Birds feed on birds, beasts on each other prey, / But savage man alone does man betray") are not by John Dryden but by his erstwhile patron the Earl of Rochester, with whom he had a bitter falling-out.
"The Marriage of Bacchus" that Purcell dislikes is an opera by French composer Robert Cambert titled: "Ariadne ou Le Mariage de Bacchus". It was adapted for the London stage by Louis Grabu in 1674. At the time, Grabu was Master of the King's Musik.
When Pepys, the Purcells, and Pelham are climbing the stairs to view the fire, Pepys is speaking lines from his diary entry of 2 September 1666.
At a height of six feet and two inches, Charles II was considered enormously tall by seventeenth-century standards. He is played by Simon Callow who is 5'7".
William of Orange is first seen at his marriage to Princess Mary in 1677. William was 27, but Corin Redgrave, who plays him, was 56 at the time.