Stumbling on the Esquire magazine Drinks Database (not a compendious collection by any means), we find yet another recipe we hadn't seen:
The lime peel looks nasty in the picture, and the ice cubes give us pause, but this is at least the simplest Singapore Sling we've seen. Most recipes we've seen call for cherry heering, not Kirschwasser, so we will have to give that a try.
1 ounce London dry gin
1 ounce Kirschwasser
1 ounce Benedictine
Glass Type: Collins glass
Stir well with 2 or 3 ice cubes in a chilled cocktail shaker, then pour unstrained into a Collins glass and fill to taste with cold club soda or seltzer. Garnish with the spiral-cut peel of a lime.
... NMC in comments finds the same confusion. I should note, however, that one blog reports that David Wondrich, presumably the author of the above recipe, published something different in Esquire Drinks, but with much more plausible proportions ... AND with Heering not kirschwasser???:
2 oz London dry ginI really wasn't buying the entire ounce of Benedictine, but now I'm of a mind to e-mail Wondrich and ask what gives.
1/2 oz Cherry Heering cherry brandy
1/2 oz Bénédictine
Stir all well with 2-3 ice cubes, pour unstrained into highball glass, and fill to taste with club soda (or ginger beer, if you're of a mind to).