Finally - the manual for the 194 GPF SPG has turned up on Gallica.
http://gallica.bnf.fr/ark:/12148/bpt6k9612676c
Lots of detailed drawings of the recoil and projectile charging systems.
There may be manuals for the 280mm howitzer version and the tractor but the search engine hasn't disgorged them yet.
Regards,
Charlie
