Re: Getting started on purchasing a SMB
If you are most interested in that particular GM Van (the one in the first post of the thread, sorry for my delayed response), the differences between the SMB and Quigley 4x4 conversion are not relevant. That one is an IFS front end. While it is still 4x4 it will have a lot less clearance than a Ford or Chevy solid front axle. It will be great for snow and sand (especially if it has the rear locking differential from Chevy), but will be less capable in other off-road situations (although a bit less rollover prone, perhaps). That it is an RB negates some of the clearance issues vs. an EB, but probably not much.
Regarding the point about not having a furnace listed, if it is a GM diesel it might have one (it is only an $850 upgrade for the Espar) and the owner doesn't even know it (I didn't know about mine).