Brother, forgive me, I've tweaked your cocktail in the quest for harmony between whiskey, elderflower, falernum, and lime. Ideally, I also add 5ml (1 spoon)...
Yes, Barr Hill Tom Cat is what I use. I also lower the lime juice to 1/2oz and increase the Falernum up to 3/4 or 1oz. I would make that modification with bourbon or tom cat as the recipe as written is too acidic for my taste.