Lots of rebuilds on line also. Google "rv rebuild" Some sites better than others buy handy info. Whatever time you think you will need, triple it. On the money side, from my experience what ever the RV place wanted, you can do it for about 75% less. Due to labor costs, but remember your putting in 3 times as long to do it. Take lot of pic's so you can put back right.
Etc... Changing to diesel, first off have you measured if it will fit? And you have to have the right transmission behind the motor to be successful. Not to mention added weight on steering. What about your state laws, are you still getting smog tested? Call up an injector place, ask them your thinking about burning veggie oil and what advice they might offer. I can tell you Seattle Injector loves those people, because they buy a lot. After and WHEN you get thru all those hurtles your going to have a RV that is so may years old and you will have a ton of money wrapped up into it.
IMO, get rv house part fixed up, keep stock and enjoy.
OK I'm joking here...Your going to have to put engine so far back for weight purposes that the 5.9 valve cover will make perfect arm rest.:B
You might enjoy looking at this site.
http://www.4btswaps.com/forum/forum.php Lots of projects there.
Also take a look at the 4bt and be sure to look at horsepower (or lack of) and RV's aren't light.
http://www.cumminsdieselspecs.com/4bt.html
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"