Jeff, I got your email but might as well say what I know here and hope that Henk or Ian can contribute from their bigger range of parts lists.
Firstly:- My own bike is fitted with the pre war combination levers which were certainly used on early M20's, but I have no idea when they where deleted.
Secondly:- I have two parts lists which both quote the same lever part numbers.
One is an MT list for contract S12424 for 8000 bikes demanded in 1941 it is the 3rd edition printed in 1944.
The second list is RAF and covers two contracts from 41-44. The two scans below are from this list and clearly show and state that the levers are not of the combination type and that the mag and air levers are the ones with the single screw pivot clip fixings.
I have saved a set of brass Amal combination levers for my own M20 in case I want to change them at some point. So it would be nice to know when, or if these were used......I expect Henk has wartime pictures.
To the most part the levers and fixings were all dull plated at the build stage, but I have seen lots of NOS boxed items in bare metal or painted.
Ron.
email (option): ronpier@talk21.com