If you've got a 91, and have an M5OD out of a 91-92 Navajo, get EVERYTHING for a 91-92 Explorer or Navajo. If you've got a M5OD out of a 93-94 Navajo and you're putting it on your '91, 91-92 parts will work, but from my experience it makes for a hard to push clutch pedal and sometimes a slave cylinder that goes bad fairly quickly. I would use the parts for whatever year the tranny is, even if the 93-94 line doesn't fit as well on the '91.
The Navajo was produced 91-94 just like the 1st gen Explorer, so just saying it's a Mazda Navajo doesn't help. If it was produced before September/October of 1992, it's a 91-92, if it was after that, it's probably a 93-94 model.
The parts were redesigned in 93-94 for the clutch issues with the M5OD, even though they didn't really fix the problem. The currently available 91-92 parts feature "revised" designs that attempt to purge air from the clutch system rather than trap it like the previous design. The big difference from the 91-92 to the 93-94 is the line design and position. The location of the line on the master cyl and the routing of the line is different, so if you use a later line or master on an older model, or the older line or master on a newer model, you'll have to deal with cramming it on there rather than an easy and simple factory fit.
I'd suggest getting all new parts. We have a member that is a Ford Dealer (FORDSVTPARTS) that gets genuine Ford parts at 10% over cost. You can get the master, slave, and line for about the same as what you'd pay for less expensive aftermarket parts. In my experience, the aftermarket parts are nowhere near as good as the factory stuff. You can go cheap, but you'll wind up replacing the slave cylinder every 50,000 miles and have to drop the tranny to do it.
An aftermarket clutch is fine, though, but you might want to ask the price just in case it's a great deal.
