One new EPC brand 3/4" bore center valve Girling style clutch master cylinder, part number 21-1530-J.  This fits:

Jaguar XK150 1957 - 1961;  cars with Girling equipment, not Dunlop

Jaguar XKE 1961 - 1974;  cars with Girling equipment, not Dunlop

Jaguar 3.8S 1963 - 1968;  cars with Girling equipment, not Dunlop