"this is the first published use of rum in a "East India" I know of, and, tellingly, this version doesn't feature in the first 1947 edition of Bergeron's guide, which only has East India numbers one and two."
Nor is it in Vic's 1946 "Book of Food & Drink," which has no East India drinks.
And if you're only putting 1 tsp of Jamaican rum in it, you might as well do it right, which is why I went with Smith & Cross.