I have an Amal 1940-1954 (inclusive) Settings and spare parts list and it says for M20. 496 s.v. M20 (ex W.D.) 1940-45 276L/1E. Also for 496 s.v. M20 (Ex W.D.) 1940-45 276C/1B. For M21. 591 s.v. (Ex W.D.) 1940-45 276P/1B. For Matchless 347 o.h.v. G3 (ex W.D.) 1940-45 276B/1J. Also 347 o.h.v. G3L (ex W.D.)1940-45 275F/1J . I do not know what the symbols mean, I hope this helps a bit.Dave.