Welcome to skoolie.net Jim! I don't have many answers for your questions at the moment, but you might want to check out how I rigged my bunk beds so they can also be used as seating (viewtopic.php?f=9&t=4959&start=165 or link to my conversion thread is in my sig line, and go to page 12). Before deciding how to rig my bunks I started a thread in this "conversion discussion" area to explore the topic of fold-away bunks, and there were several good ideas from the peanut gallery: viewtopic.php?f=11&t=4962&p=42990&hilit=+bunk%2A#p 42990
Don't forget the Cummins 8.3 if you come across one. The DT466 has a smaller brother, the DT360. I would pick an 8.3 or 466 first, 5.9 second only because of displacement.