You need to know when the PHH has been replaced (Pesky Heater Hose), whether the Birfields have seen grease recently, how much rust is on the undercarriage, if the Head gasket has been done and when, and just general maintenance items.
Turn the wheels full left and right and be aware of any clicking noises.
Have you driven an auto Series 80? Don't be surprised if the shifting seems "soft". They do drive somewhat like a greyhound bus. Punch the overdrive button to make sure you have all four gears, and that overdrive turns on and off.
Make sure all the 4wd modes work properly.
Damage history?
You are just down the road from me. Wish I could come along.
Drew