First things first here..
Diesels don't use a big block bellhousing, its pretty similar, but not the same.
Early rangers with diesels were mentioned. They aren't great motors, but they do get exceptional mileage in those little trucks, and the turbo version make pretty decent power(in a ranger), The one my buddy has knocks down a solid 33mpg, and even has pulled a few trailers in its day.
One option you may want to look into, is 80's Lincoln mark VII's, they could be bought with a 2.4L BMW turbo diesel. I know they were backed by a 4 speed auto, though I can't recall if it was a AOD, or a german tranny.
Another really good source is the smaller mercedes diesels, mainly for the size and weight.
Allthough, if it was mine, I'd be looking for a 4BT cummins.