True. You’ll need a plug. That’s the advantage of a SYE kit. You should be able to get a plug kit from a part store.
When you put adjustable upper arms on it you will need to take the TC spacers out
Raising the transfer case will not change the pinion angle. It will just increase the angle of the shaft to the pinion.
Another option, pull rear shaft and drive with front shaft. That will rule out rear angles if vibration remains.