I was Googling the Cummins 4B and this site came up:
http://www.4btswaps.com/forum/showthread.php?t=1076 The link has topics on just about EVERYTHING for a 4BT...... Figured I'd share it.
Edit-
That ebay link, I saw that one. But the one last week was some diesel engine out fit. As I mentioned, it was a 4BT that was used in a bread truck. I'm thinking that it'll show up sooner or later....
My 'idea', if it'll ever get off the planning and RnD, is to find a big Bolt, about 2 ton and swap in a 4BT into it. I don't want to modify the original frame or mess w/ the steering box relocation/redesign. I'm thinking a 4BT would fit in the spot a old 270 or 302 I6 GMC quite nicely.