I wrote another response but got sidetracked.
Change the oil in the transfer if you wish.
You should be right for space, but a set of ramps may make life easier.
Based on a sierra but, I would just remove stuff that may be in the way.
Disconnect the battery, remove the starter motor.
Pull the front driveshaft out, remove the jackshaft, remove the exhaust if its in the way.
Remove the gear stick, and undo the clutch cable.
When the gearbox is out, pry the seal out and tap a new one in.
A sierra FSM should have the relevant torque etc for the bolts.
In the bottom I linked my google drive with some FSM that may be helpful.
viewtopic.php?f=1&t=3445Consider doing the rear main on the engine and check the clutch while you're in there.
The hardest part is centering the clutch when the motor is in the car, but you can make a clutch alignment tool pretty easily.
Hopefully it's just the seal