I've never seen one of these. It's a dressed up Land Cruiser. Oh and 13 city, 15 highway MPG! It look a lot of fuel to push that thing 206k miles!
I don't think it's going to be all that sensitive to what oil you use. If it's had a steady diet of synthetic then keep on with that. With how much it holds I'd probably buy 2 gallon jugs of Mobil 1 or other syntheric HDEO in 5W-40 for each oil change.