A bit more info. The adaptors for the Cooper and S twin carb setup have a bulge on both sides of the adaptor (Part No 17H8379) where it bolts to the carb. The single carb adaptor (Part No 27H1389) has a bulge on only one side.
Why you may well ask? The single HS2 fitted to 850/998 motors generally has only one passage to the underside of the piston chamber and it is on the left when looking into the carb intake. The twin carb setup has LH and RH carbs and the passage to the underside of the piston is on opposite sides on the LH and RH carbs. So the adaptor for the twin setup is made to suit either LH or RH carbs. However it becomes a bit more complicated as later S twin carb setups have LH and RH bodies which each have 2 transfer passages to the underside of the piston. These are generally called "Quick Lift Body" carbs. They are used in conjunction with Quick Lift pistons which also have 2 passages on the underside of the piston face (where the needle goes in). Earlier types have only one hole and its on the vertical face of the downstream side of the piston. It gets even more confusing as quick lift pistons were introduced before the quick lift bodies.
The quick lift pistons and bodies presumably were introduced to give better acceleration, fuel economy and reduce emissions? as the pistons would lift faster and not restrict airflow as much as non quick lift assemblies. At least I think that was the reason. Any body got any further info on this matter?
So depending on what carbs you have, as the DOC says, you may only have to modify one adaptor to make it fit a RH carb or 2 adaptors to fit LH and RH quick lift bodies.
Not sure if this helps or hinders.
Regards
RonR