Hoi Arjan (and rest of the members),
I`m also from the Netherlands and own a 45" (civilianized outfit).
Got any questions, just ask. It may pay off to visit sites of Dutch dealers and mechanics. Also check the 42wla yahoo group, although strictly for WLA/WLC in original(=military), you may find it useful for tech questions.
www.flatheadpower.com has a lot of info, and dudes that know their business with these old beasts.
Hoekstra from Gameren (near Zaltbommel) is a flathead specialist, and has a large inventory of NOS parts.
www.45partsdepot.com sells both NOS and fmc parts, plus Kurt and Wendy are both friendly and helpful. (skills that some dealers really lack!!).
Jan-Willem Boon has possibly the largest inventory of NOS parts in Holland (and maybe Europe). Larry Elias from Schoonhoven also is a seasoned specialist.
For restoring a 45" WL I recommend Palmer`s 'How to restore your Harley-Davidson'. It`s the Bible for a lot of guys who want to restore their bike (it sure helped me).
Maybe you already know the resources for the restoraration of a WL, maar dubbel genaaid houdt altijd beter.
Good luck!
Flatheadrene