There are a ton of different CV's mostly per motor but Kevin and i were just talking about this yesterday they are sometimes at random.
4cyl, 12v V6, 12v V6 5spd, 3.0 SOHC 24v, 3.0 SOHC 24v 5spd, 3.5 DOHC, 3.5 SOHC and then some have slight interchange between them, as in the splined ends will be the same but the cups are different or the cages are different. I have a 3.0 SOHC axle in a 3.5 SOHC cup, the cage is much smaller but the bearings are the correct spacing and size for my cup. I couldn't fit the DOHC birfield in the SOHC cup.

NOW my brother in law bought reman CV's for his '93 and i bought remans for my old '94, we got the same part number and brand. His left CV was too big and my left was too small, our parts were delivered at different times to different addresses and they were remanned by the same company with the same part number on the boxes yet we still got different axles.
I think the aftermarket just thinks all montero's are the same. Having said that OEM only junkyard or dealer, everything i've put on my truck that wasn't OEM either didn't work correctly or didn't last. It's cheaper to use the OEM stuff.