Hi Clive,
Thanks very much for those links. By happenstance, I was just reading your EMLRA articles on the same subject, which look to have been formed from the same sources.
If I'm reading them correctly, it looks as if REME units assigned to Divisions (HQ, and Bde Workshops) in the BAOR used the same serial number scheme they used in wartime up through 1959.
In 1952, additional serial numbers were assigned for HQ REME (70), Corps Workshops (71), Recovery Units (72), and Medium Workshops (73). If I'm reading that correctly in concert with a tidy information paper I found on-line about REME, this mirrored the basic US logistics and maintenance system (or vice versa as the case may be), where the Divisional workshops performed 2nd echelon tasks (general maintenance), the Medium Workshops performed 3rd echelon tasks (repair), and the Corps Workshops performed 4th echelon tasks (overhauls/re-builds). But I'm not sure about Base Workshops. Is that term synonymous with Corps Workshops? Or would the Base Workshop level vehicles be a 5th echelon and wear a '70' for HQ instead? My bike was rebuilt by Base Workshop 4, so I am keen to understand that.
Then, in 1959, it looks as though the entire serial number system was revamped and expanded. HQ REME Corps Troops became 260, Medium Workshops were assigned 262, 262, and 264, Arm'd Recovery Units were assigned 270 and 271, Inf. Recovery Units to 274 and 275, and Tels Workshop got 279. (Incidentally, what does "Tels" refer to? The only thing I can think of is 'Transporter erector launcher', which I suspect is not right.)
In conclusion, it looks as though if I want to portray my BSA WD M20 as belonging to a 1950's era BAOR REME line unit, I should use 40, 88, 89, or 90, and if I want to portray it as a Base/Corps bike at a Base/Corps level workshop, I should use either 70 or 260. Would you agree?