Thanks for the link Tom. Great page. I had definitely discovered it already and I believe I even downloaded the schematic for the 761 from there last week.
I've been searching for the others for about as long, but they are proving a little more elusive. I'm thinking I'll have to secure a membership on radiomuseum and ask around on there a bit.
I came across a this very detailed site last week in Italian which covers one gentleman's restoration of a Grundig 4090:
http://www.casaparadiso.it/radio/Grundig_4090.htm
I may tackle the 761 first just because I believe it will be the easiest and I have the schemitic already.