Mike
If you have your heart set on a Volvo (I like them) I would look for a 610 (mid rise). The number designation relates to the length of the sleeper.
I agree that keeping the tandems is probably the right idea.
I would be happy to quote a conversion for you. Before we go any further, you should know that it takes from 6 - 8 months to complete them. We take the time to make them right.
My contact information is on our website if you want to talk.
Tony
www.toolsetmotorhomes.com