Allister
The diagram at the bottom Shows a diagram of a Distributor Cap to replace Lucas 400316 which is the serial number stamped on my Lucas Cap. My email address is davidselfridge52@icloud.com
Bernie the Cap in your Photo looks like the correct one, could your check with magnifying glass inside for Lucas and serial number or take a photo and zoom into the 2 small flat areas adjacent to where leads protrude for the Stamped Number
Davy
David Selfridge