Say, Phil — do you still have that extra SVX cage? Can you post some pictures? I'm curious how the antenna(s) connect.
You mentioned having chopped off the connector from the UK SVX radio. Were you talking about the one wired to the back of the cage that connects to the car's harness?
The first picture in the German RD25 PDF
almost shows it
Even if that's the one you cut off, I'd still be very interested to compare the UK cage to my pictures of the US one.