Sloe gin comprises such a large part of this cocktail that the style and quality of your sloe gin will dramatically affect the finished cocktail. Choose...
I've found a recipe for a cocktail like this that dates to between 1853 and 1942. These were the years that the Mi-Ho-Loong or Shanghai Volunteer Corps existed. Their cocktail was a quarter of a Gill of Sloe Gin, an eighth of a Gill of dry vermouth and a dash of Orange Bitters. https://chinarhyming.com/2016/11/03/shanghais-mih-ho-loong-cocktail/
https://chinarhyming.com/2016/11/03/shanghais-mih-ho-loong-cocktail/