Just my opinion, If you want the new syncros, get the new box. If you have very little wrong in yours, replace what is needed, not everything. On my 94 Mighty Max the main shaft moved for/aft with throttle changes in the upper gears, there is a rear bearing retainer that has loosened fasteners. I could not get the time to take it off the road so I would keep a finger on the shifter when I had to lift throttle in that gear, irritating. Frame rust made the decision to park a very economical tow rig.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.