Buy it from a cruiser shop. If you have a question during install, they'll be able to set you straight. A parts jockey at an online Toyota parts store will be worthless
That threaded NPT plug was installed the second time around- 20 years later. The first time, I plugged it using a big fat short bolt, washers and nut and snugged them up tight. Ran it like that for 20 years
The hole is tapped with a NPT tap that will be able to cut threads for that size. The brass plug is NPT. Don't know the size but there's only one size that will be the obvious choice. A machine shop did it for me.
To answer one question:
The 4 speed has a big mounting bolt that goes through the front of the transfer case plate. That bolt isn't used in the 5 speed so the bolt hole needs to be plugged otherwise oil will migrate between the two cases. The best way to plug the hole is to tap it and screw in a...