The external slave was used on the ax15 from 94 till they changed transmissions. The slave, line, and clutch master cylinder are all one part it can be found seperated at 4wd hardware and some other places.
Things to consider when making the swap.
The push rod length.
The push rod hole that connects to the clutch will need drilled larger if you use the new master cylinder.
The master cylinder bracket will need drilled and ground to fit on the studs and around your bulkhead electrical connecter.
The pilot berring is not the same size.
The transmission is 23 splined output vs 21 like a BA10 so you will have to change the input on your transfercase or pick one up with the AX15.
Keep this in mind as well, the np231 you have on the BA10 may be clocked more one way vs the other so you transfercase hang lower or higher.
Depending on your transmission / transfercase clocking your 4wd shifter may need modified to fit.
Last, your transmission mount will need modified or your skid plate. I cut the orignial ax10 mount and welded/bolted the ba10 to it. It was the only way I could match the holes in the skid plate to the ones in the ax15 since it came out of a mid 90's jeep.
2010 Jeep Liberty > Stock < wife's
1989 Jeep Wrangler > 4.0 conversion, 4" lift, 33's
1985 Jeep CJ7 > AMC 360, 4" Lift, 35's, locked front and rear, winch, Onboard Air, ect..