Take, for example, The Great Train Robbery (1978). Starring Sean Connery and Donald Sutherland, it shows the painstaking preparation leading up to the first-ever robbery of a moving train in England in 1855. There's a shipment of gold being transported to pay the soldiers fighting in the Crimean War, and the crooks must secure four keys to open the safes on the train before they can actually pull off the heist. I love the great period costumes and sets, there's wonderful humor throughout (but not enough to turn it into a farce) and both Connery (who did his own stunts, including running along the top of a train going 55 mph) and Sutherland are spot-on as the calculating rogues orchestrating the robbery. Bonus points for the twist at the end.
I would argue that The Man who would be King (1975) would also fall into this category. Again starring Sean Connery, this time paired with Michael Caine as a pair of rogues who want to set themselves up as rulers of the nation of Kaphiristan (in the region of Afghanistan). This time we the Victorian period is represented by the British Indian colonial experience, with our two rogues being ex-British soldiers out to make a fortune for themselves. The set-up involves the big con they pull on every local warlord they meet, but naturally things can't go well indefinitely. Again, lots of great humor, but not a farce by any means.
Harry and Walter go to New York (1976), on the other hand, does dip more into the musical comedy end of the spectrum. It features James Caan (!) and Elliot Gould as a pair of would-be vaudevillians who decide to pull off the world's greatest bank robbery after escaping from prison. In so doing, they cross paths with Michael Caine, a gentleman celebrity criminal adored by all. It's a great wild romp of a movie, and the scenes of Caan and Gould doing 1890's song-and-dance numbers is worth the price of admission alone. It's not what one might call a "good" movie, but it's fun, and the sets and costumes are first-rate.
The inverse of the genre is, of course, best served by Sherlock Holmes. Aside from the straight adaptations of the original Holmes stories (I personally prefer the Jeremy Brett versions that were originally shown on PBS from 1984-1994), the 1970's came up with two very different takes on the character. The Seven Percent Solution (1976) features Nicol Williamson (who played Merlin in the film Excalibur) as Holmes and Robert Duvall as Dr. Watson. The real "caper" here is Watson's plan to trick Holmes into going to Vienna to meet Dr. Sigmund Freud, played by Alan Arkin, to assist with Holmes' addiction to cocaine. Naturally, they stumble upon a real mystery while in Vienna, and the two plots intermingle nicely. A lot of excellent performances here, not without some humor (in particular the tennis match between Freud and the villainous Baron Karl von Leinsdorf, played by Jeremy Kemp).
Finally, we come to The Private Life of Sherlock Holmes (1970), which is less of a "caper" film than a more traditional Sherlock Holmes adventure, but which I nonetheless feel deserves inclusion here for its pitch-perfect presentation of Victorian London, even though the film has a decidedly... goofy quality in places, as if it couldn't decide if it wanted to be a serious movie or a comedy. Robert Stevens stars as Holmes, but I think Christopher Lee as his brother Mycroft steals the show. It's also one of the more fantastical Holmes adventures I've seen, bringing in the Loch Ness Monster of all things, and the film is (in)famous for its inferences regarding Holmes' sexuality, but for all the baggage I still enjoy it.
There are, of course, other Holmes films from the 70's, such as Sherlock Holmes in New York (1976) starring Roger Moore as Holmes, and Murder by Decree (1979) with Christopher Plummer in the role. There's just something about that era, and the way it was depicted in the 1970's, that has a certain authenticity to me that later films, even though they strive for just as much historical accuracy, just can't match.