Try this Needle Comparison Chart | SU Carburetters
This one talks about needle options for Minis with various carb setups, including single HS6 SU Carbs - Quick reference needle selection (for Minis)
The EA71 is very short stroke, so BMC/BL long stroke stuff using single HS6 may not be much help, however the Austin Maxi 1500 and 1750, B-series 1600 and 1800, and O-series 1700 might give some ideas of needle options.