http://www.dieselbike.net/privateconversionsI-Z.htm
Some interesting rides on this page that members of the DIY persuasion will find interesting.
Some mention of fuel economy stats as well, with various numbers chucked around (usually without any context, unfortunately) like 300, 140 ,120...
I love this chopped Honda with a Yanmar conversion.
There are tons more pics & specs here:
http://www.dieselbike.net/privateconversionsI-Z.htm