I had this combo in my '77 CJ5. Definitely the syringe deal. Avoid the hassle and mess if you do it without it.
One other thing you might want to search is the additive in the gear oil. GL4 is what you want to use in straight cut gear applications (trans and tcase), especially use where yellow metals are present (synchro gears in a transmission).
Open the fill holes first, then have pan/funnel ready to catch used fluid when undoing drains. Then drain both. Button the drain holes back up and fill with fluid until you can feel fluid with tip of finger just inside fill hole or it starts to come back out. Button up the fill plugs and you're done.
The tranny drain is on the front near the bottom. The fill is on passenger side near the...