I have come across an aluminum slave cylinder in the aftermarket. It is available at Advance auto parts, TECHnovation part#360047, listed as a '98-2001 XJ part.
http://shop.advanceautoparts.com/buy/products/384486-1998-2001-jeep-cherokee-technovation-clutch-slave-cylinder-part-360047.htmlThe factory slave cylinder for the external slave bellhousing, and most of the aftermarket slaves, are made of plastic, have funny "pin & o-ring" hard line retention, and no bleed screw. The aluminum cylinder still has the funny hardline retention, which can be worked around through Advance Adapters(no relation to Advance auto parts) -3AN adapter fittings(Product #716130IR,
http://www.advanceadapters.com/products/716130ir--716130ir-42quot-stainless-steel-hose-and-fitting-for-1987-1996-jeep-yj-wranglers-with-internal-hydraulic-release-bearings/) The newly available aluminum slave cylinder does not have a proper bleed screw, but rather has an allen-head set screw. The threads of the set screw match those of a bleed screw, so a proper bleed screw could be installed in place of the set screw. There is a small passage drilled into the side of the casting where the set screw is, but that could be plugged with a very small set screw.
All this comes into play if you are doing an AX-15 swap into your car using an external slave bellhousing.
Just as a reminder, if your transmission came from an internal slave application('88-'92-ish Jeep), you will need to swap the input bearing retainer out for one designed to carry the throwout bearing for the external slave setup.
Another reminder, you do not use the stock Eagle flywheel or clutch - the flywheel is too thick, and the clutch will not engage(it'll always be disengaged, even with the clutch pedal released). You use one for a Jeep 4.o application, best sourced from the year model of your transmission's source, or one that featured the external slave, which is anything newer then '93 Jeep.