I removed the huge r chokes and replaced them with some smaller ones.
I ordered some chokes, the type that are really just stiff wire with some ferrite moulded on to them
I measured the XL at HF, typically 40 ohms, and about 0.5 ohms down at 100Khz.
Presumably lower at the 1pps and 9k6 data, and the GPS now works properly ;-)
For info, the symptoms of having too much inductance in the GPS leads was erratic 1 pps heartbeat showing.
For example, maybe every 10 beats there was a 2 pps or similar, the calibration windows whizzed by in a few seconds ,
despite being told to do a calibration for 20 seconds, and occasionally times reported such 104:31:23 UTC !!
So now we know.
73 de Andy