Hydraulic clutches have been around since the late 1950's, possibly before that. My 58 Austin Healey 3000 had one, also the 57 MGA I owned. Ditto for the 65 Dodge D-100 pickup with the 318 V8 I used as my first Diesel truck road service vehicle. All of those had a slave cylinder mounted outside the bellhousing, and a regular threaded clutch adjustment. The ones that fit inside the bellhousing aren't adjustable, and they rely on the proper spacing between the front of the transmission bearing retainer and the flywheel friction surface to work properly. The explosion-resistant scattershields the drag racers used before they got smart and started running automatic transmissions were some of the first ones I saw with the internal slave cylinders.

Edit: Spacing the flywheel back could create problems with the starter pinion gear engagement- - - -there's no free lunch!
Jerry



"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!