You'll not find anyone with a greater depth of knowledge about pre-war Sunbeams than Bob C-C.
Both his books are about but at wildly varying prices; When buying the ' Illustrated History' watch out for poor binding, its poorly produced and prone to falling apart, at least mine has.
I doubt even the VMCC has any more guff re Sunbeam than Bob has written; the pitman book is but a guide only,
Meanwhile I found this on U tube which is handy
https://youtu.be/sPxsZ_HxU1U,
Its worth while learning to set the clutch up, and get the plates re corked; on my Model 1 I also got the clutch spring studs made larger, a worthwhile mod.
I see you have also found the yahoo group site, be nice to liven that up a bit.