The Book that you have referred to is part of the "Jezt hilfe ich mir
selbst" or "now I help myself" series published in Germany, only in
German, by the way.  I have looked through the book, and while it does
have a few pages on roof conversion, it deals with high-top roofs
mostly, not what you have in mind, that is, moving a roof from a Westy
to a conventional van body.  The book has pictures and plans for using
cabinetry from German manufacturers, mostly a firm called REIMO.  In
short, this book probably won't be much help to you.

Body shop experts usually look at the best way to do this job as being
to cut the support posts somewhere in the middle and move the whole roof
assembly over.  This is the way they deal with damaged car roofs
generally. I have considered having this done, and have been quoted
$1000 for the labor & materials in Iowa.

I did a poptop conversion on a Syncro van myself for someone a couple of
years ago.  It wasn't that hard, and turned out well, and the owner has
been satisfied with the vehicle, which now also has a Subaru 2.5
engine.  I just cut the center section of the roof out with my plasma
cutter and mounted the Westy roof on top.  I made a wooden platform
above the roof at the rear to give a flat sleeping surface.  It cuts the
clearance so that the front pad for the upper bunk has to be carried
below.  I trimmed the cutout area with the same gasket strip that is
used on the front section of the poptop, or luggage carrier.  You end up
with a fake Westy with a conventional headliner, which is nice looking,
& a bit warmer and quieter than the real thing.  You can keep a full
width lower bed, which I prefer personally, and add as much or as little
other cabinetry & fittings as you want.

Chuck Hill