Mixologist, cocktail historian, and tiki cheerleader Martin Cate documents the recipe for the Twenty Seventy Swizzle in his fantastic book Smuggler’s Cove, where he explains that the name came from the two rums he used: Angostura 1919 (a vanilla-tinged column-still aged rum) and the inimitable Lemon Hart 151, a fantastic overproof Demerara rum from Guyana.
There’s no need to restrict yourself to numerologically-correct rums, though – we’ve made it with a variety of aged and overproof Demerara rums, and each one somehow ends up tasting better than the last. That might be the 151 talking, though.