Under the hood, or under the car. Trucks and SUVs only.
A used transfer case is priced on 159 generations across 52 nameplates, listed below by make and model. Open one for the asking price on that car and what else the part fits.
A transfer case is heavy and comes down from under a truck that is sitting on stands. Bring a helper, and ask the yard how it wants one lowered.
Typical sizes, not a promise for every car. Everything to bring to a pull-your-own yard.