I don't think all the changes H-P posted will be necessary. A couple of good references, particularly for early Kübelwagen are two Allied publications, both since reprinted.
The
BIOS report on the Volkswagen and the US technical manual
TM E9-803. The latter I think is available as a PDF for free but the image quality isn't the best. Maybe adequate for what you need though.
Which kit are you using as a base?
I would suggest either the Hasegawa/Bego or Tamiya DAK versions. The latter may be easier to find.
In brief, your main issues will be new exhausts, shortened rear mudguards, fill in holes for jacking points, relocate horn (and add extension as per photo) and shovel, fit trafficators onto the sides of the windshields.
I think that's about it.
Cheers,
Sean