Alistair, that is something I am not sure of. I have a Bagnold Sun Compass on my 1940 LRPG WB Chev. Here are photos of the Bagnold and Cole Sun Compasses for those who do not know what we are talking about..
Cole Sun Compass.
Bagnold Sun compass missing it's centre needle.
Instruction sheet for the Bagnold Compass.
The mount on a preserved Lynx.
My mount opened up a bit. My Lynx was on loan to a Museum for a while.
Sorry, I'm not much help but will make some enquiries.
Cheers Rick.