This is the first time that Shaggy drives the Mystery Machine.
Despite the title, the story is not set in Scotland, where Loch Ness is. Scooby and company later go to Loch Ness and meet different versions of the legendary Monster in A Highland Fling with a Monstrous Thing (1978) and Scooby-Doo and the Loch Ness Monster (2004).
The ghost of Paul Revere rides around yelling that "the British are coming," an image which comes mostly from the 1860 poem "Paul Revere's Ride" by Henry Wadsworth Longfellow. The real Paul Revere rode through Boston silently, only knocking on certain doors to warn individual allies that "the *regulars* are coming," as Revere and his neighbors still considered themselves British. Longfellow was using poetic license to create an American legend.