My experience is with putting my SYE. If you take the back cover off, there will be two big main shafts with splines. Each will have gears pressed down on them with c clamps holding the gears in place. You will just grab those two shafts and wiggle them out of the t-case. Have a piece of cardboard ready on the floor or a big rag layer out on a workbench so you can put it down on that once the shafts come out. The, just change the chain and replace. The whole t-case does need to come off at all.
I am working on mine today, hopefully getting the SYE collar sealed and filled with oil, I'll have a more clear memory of it then.
Big thing is getting those yokes off the splines as I remember. Air tools make nice work of it. Make very certain of how your t-case oil pump and pipe are connected. The guy that I bought the SYE from had put it together and not made sure the pipe was in the pump and you could see that there had been some drying out and overheating (SYE uses plastic speedo gears and they were melted into a glob)