At this stage I was then able to start testing. The system worked, amazingly, but I couldn't get a decent speed out of it without generating 'Gross Positioning Errors' Fairly obviously the servo card needed tuning, and some parameters tweaking in the control. However the good bit was that the gearing and encoder interface was working correctly to give me 360 degrees for a full turn as it should.
I went through the Bosch manual MANY times following their procedure, and try as I might couldn't get the main servo motor spinning more than about 700 rpm without errors - it's max speed is 3100 rpm and I'd initially set it up to max on the servo at 2000 to be on the conservative side.
Many people offered help, both from this forum and others and I thank them profusely, but the break through came the other day, when by chance I was put in touch with a local chap who had installed this type of servo card many years ago.
Long story short - he came round yesterday, and after four hours of tweaking, un-tweaking and head scratching we got it to a very acceptable performance. Servo motor is now reliably able to spin at 2500 rpm giving 2500 degrees a minute on the table.
So to celebrate, last night and this morning I made up the swarf cover and am ready to put it on the machine table and try it for real. That won't happen immediately due to family commitments