Posted this information in thread for Muttsjet #642 but figured it also belonged as a standalone post for all to learn and benefit from! Steve
HERE IS INFO FOR ORPHAN AUTO- JIM 1-937- 554 - 6 000
This cylinder is described as: " 3/4" Bore, Center Valve, Remote Reservoir"
You will likely need to reuse your original pushrod. Aprox $75-85 Feb/24
Advise if you need a pic' of what the original should be.......or search the forum.
Original markings on #878 Clutch master: EHEB-7707 and #310680 CC3
Rebuild Kits: Raybestos CMK1936 (1983-88 Jeep Eagle, 84-86 Jeep Truck & Wagon applications) Girling SP1995/2 MANY Triumph TR2 TR3 TR4.
Both of the above kits are getting harder to find. eBay is presently a good source of old kits.
Pictures below are of original unit from #878. Relined with brass insert by vender now closed.... 
Seal in above spring is usually main failure- #64673407 is number directly on seal. Seal can be found in many other Girling specific .750" kits (see note below also!)
Specific Seal# 64673407 First replacement part I ever found for my Goose! Popped out of the 3rd box of seals I was looking thru in the auto parts store! BINGO!!! I'll take it! 1996 or 1997!
JUST IN!!! While looking for the above seal, which is usually all that needs replacing I found this exact seal in a LUCAS SP1967 kit on eBay for about $15!!! It has extra parts, like reservoir cap and washer, but barring the ability to get the SP1995/2 kit, this would do the trick for you and it's cheaper and new!