This handy chart was in an Accessory Mart catalogue in the '90's. It is copied with permission.
I asked Tony at Domiracer / Accessory Mart for a copy so it could be posted on websites.

This appears to me to be a condensed and simplified version of another document.
That work is 6 pages of data apparently copied from Enfield's engine factory records in 1970.

Some important notes must be included with the chart :
1. It is useful for determining year and model of Enfield twins from the engine serial number. Similarly, gearboxes can be dated.
2. Being simplified and condensed, it is incomplete and contains errors.
3. Dates are for engine build, not bike build or dispatch.
4. 750cc Interceptors are referred to as 750cc Super Constellation, something only the engine factory did.
5. Enfield dispatch records provide more complete and reliable information.

Chris Overton