Gangway! can be pretty easily encapsulated as a historical heist comedy novel or for those of you familiar with Westlake, Dortmunder in 1870's San Francisco. It also reminded me a lot of Westlake's comedy capers like High Adventure. If any of that is up your alley, then Gangway! is probably worth putting on your list.
The protagonist, Gabe Beauchamp, is a con from Hell's Kitchen, forced to go to San Francisco by his local ward boss. A lot of the book is about Gabe hating and adjusting to what he considers living in the boonies, though the authors go a long way towards making it more of a mockery of the New Yorker who has never left Manhattan. Gabe has a nose and a skill for crime and is immediately attracted to the Federal mint and the wagonloads of gold bars that are shipped into it from the mines around SF (this is the late gold rush period). So he assembles a string of wacky characters, including a streetsmart San Franciscan women who takes a shine to his exotic east coast ways.
He comes up with an elaborate, dubious plan that very much invokes the title of the book and involves a lot of other interesting characters and wacky situations. I found some of the humour a bit forced, just not quite as tight and polished as the Dortmunder novels, but it never gets in the way and overall supports a light, pleasant tone that makes for quick and enjoyable reading. The heist itself is quite fun and would have made for a great movie.
There is a great interview with Brian Garfield (author of Death Wish among many other things) and he talks about his days in the 60s and 70s playing in a regular poker game with Westlake as well as how they collaborated on Gangway!
Don Westlake had a blinding-fast mind. He always seemed to have on the tip of his tongue the sort of wonderful witty rejoinders that occur to most of us a day or two too late. In 1970 we got the idea that it would be amusing to try combining our strengths in a Western comedy novel. We wrote Gangway!, and it turned out to be quite funny, I think. Henry sold it and it did fairly well. But our ambitions to sell it as a basis for a movie didn’t work out. And we’d done it in a silly way—each of us would write a draft, then turn it over to the other, who’d rewrite the whole thing and give it back. It was about four times as much work as either of us would have put in individually on a book. So we didn’t try that again. But it was fun, and we got to know each other’s working styles.