After skimming through this document:
http://faculty.sdmiramar.edu/wnorth/249/249six.pdf
I am not so sure what this last supercharger is for. If someone can provide more accurate drawings maybe it will be more clear. I can't make out exactly how it works from the pictures posted.
And the added bonus is the fact it is already and hour past midnight here. So I will continue this discussion tomorrow.
EDIT: Something like this:
