Well, thanks to m0ngr31's thread
ASIN info, we now know that the ASIN of a pBook can be used if Amazon does not sell a Kindle version.
I tested a freebie I got from B&N called "
Deadly Sanctuary" by Sylvia Nobel. It is the first book in a series and is only available as a paperback on Amazon. The first version of book I found did not have an ASIN number but I found copies being
sold by individuals on Amazon did have an ASIN.
I followed the same procedure using the Mobi2Mobi GUI (with K4PC and K3) and it worked just fine!
I'll be updating the wiki accordingly.