[evan9eleven]

Scope creep? More like scope avalanche... ask me how I know.

If you are going to do synchros, you really should replace the sliders too, as these and the synchros wear into each other over time. Change just one and the shifting may not be optimal. Once you get into the box you will also see what else is worn. Differential housing bearings may need changing, if the pinion shaft bearing race is loose the case will need machining. And so on. You really don't want to tear it apart again anytime soon, so if you can justify the cost it is definitely better to rebuild it all at once.

As another poster mentioned, there is lots more to consider while the motor is out. Fuel lines, motor mounts, CV joints, shift coupling, valve adjustment, cleaning and sealing up leaks, etc.