Unless you're looking to swap drivetrains right off the bat, pay close attention to the condition of the engine, transmission, T-case, and axles. Considering it costs as much to rebuild a Jeep L- or F-head four-cylinder as it does to rebuild a Chevy V-8, making sure the engine you start with is in good shape and is worth the effort. At the very least, pull the dipstick and check for water in the oil. Hardcore buyers may want to pull the drain plugs in the tranny and T-case to check for water as well. You can usually just remove the fill plugs in the axles and check fluid condition and level with a flashlight or your finger.