Wen Mac lineage

Sorry if this may be an old subject, but my search came up beans.
I am interested in the Wen Mac engine lineage.By cast model number is my standard.
As best as I can tell, there are EIGHT named variants; of course within each named
variant the are surely un named deviations.
So forgive my lack of knowledge. I started collecting Wen Mac motors that I had as a kid about 2 years ago.
This has been a lot of fun for me, and a rewarding experience. Here is my knowledge of
cast model numbers;

MK 1 (or first model) - Just cast "Wen Mac" on port side. No MK#.
MK II seems to be the most available model. Many variants as I see them.
MK III
MK IV
MK V
MK XI- very elusive. I recall seeing one a few years ago but this is one I am still looking for.
MK XII
MK XIII

Notice lack of MK VI,VII, VIII, IX, X, if my search is accurate. I don't know if Wen Mac produced any
engines bearing these model numbers.

There was an extensive history of pretty much ALL Wen Mac engines on Mark Boesen's .049 collectors Group on Yahoo.

I've got a copy of it buried in my drives and will post if I can find it, or maybe he will check in here.