Dating Singers and the wife will not be mad at you.
Pre War Singers
Post War Singers
The letters following the chassis number as well as some of the unit numbers (eg the engine, gear box, rear axle, etc) indicate the year of manufacture on post war Singers.
The serial number is just behind the right front suspension, I am working on a drawing for ALL Singer's to show the location of all the number.
Total production = 11,950, Left Hand Drive cars have a 'L' prefix so the number would be L4AD. Twin carburated cars have a 'T' in the number as in 4ADT.
Take for example an SM 1500 roadster with chassis number 4AD3024 X, engine number 3046 W, gearbox number 3090 X and rear axle number 2957 X.
The car is a 1954 ("X" chassis number), but the engine is a 1953 ("W"). The gear box and rear axle are both 1954 ("X").