The Abbey cocktail was first published in 1930 in "The Savoy cocktail book" by Harry Craddock, the original recipe is composed of 50% gin, 25% Kina Lillet and 25 % orange juice (without forgetting the dash of angostura bitters).
* The Kina Lillet no longer exists, you can replace it with "normal" Lillet. The Lillet does not contain quinine and therefore radically sweetens the cocktail, the original spirit is no longer really there but it is the best solution today.
It is also for this reason that you can find arranged Abbey recipes in which the Kina Lillet is replaced by vermouth. In any case, tasting abbeys will always ring a bit false in the absence of Kina Lillet.