These photos and notes are supplied by Klaus Junker:

There was in the Twin Cam Yahoo Group a discussion about locking brakes on a TC. Part of the discussion was, which parts are fitting in a TC Master Brake Cylinder. There is in Germany a former machinist who works since 30 years in the Dunlop-Girling and the later company organization in test and experimental work. He has a lot of old parts and explained me whats going on.
The only real request is the diameter of the piston. This means, that the inner parts of any cylinder which has the correct diameter is usable for an TC. And he showed me, that even a cylinder which is used for the clutch is fitting for the TC MBC. The inner parts of a Jaguar cylinder have the same diameter as the TC and you can use it.
For explanation I add some pictures. One shows the used parts in newer style. The next shows the today's Girling replacement parts. The third is a picture of the Jag cylinder with detailed parts and the fourth is the content of the rubber replacement parts and the correct number of the package.
Regards Klaus

Used parts in newer style removed from a Twin Cam master cylinder.


Current day Girling replacement parts.


Jaguar cylinder with detailed parts.


Contents of the Girling rubber replacement parts.