I've cracked the case. It turns out that the combination service manual is riddled with errors. Many of the measurements given apply only to the Beogram 8002, not the 8000.
I have got a copy of the service manual for the Beogram 8000 specifically and it says only to adjust the platter till flush with the top. This I can do. It also incorrectly gives a sensor arm height of 19.5mm when it should be 23mm for the Beogram 8000.
Please see the attached screen capture of the correct service manual.
Cheers,
Gnab