Emma Steed, being an English spy, is an obvious homage to Emma Peel and John Steed, from the British television show The Avengers.
Characters are worried about a US war with Spain. Such a war began (and ended) in 1898, just four years after the installment is set.
Final episode without Whip Morgan.
When Pete Hutter whistles with heavily gloved fingers, he's repeating a gag that Stan Laurel used in "Way Out West."