I have an extra earth strap left over from my 500 rebuild.
Its exactly a foot long with a 6mm battery type connector at one end, the other end is a flat 6 mm terminal the cable is 7.5 mm o/d including the insulation so pretty hefty.
I recall thinking at the time that it ws a good idea - so far no trawls of my dismantling photos have come up showing it.
I can't remember where it was fitted as an extra earth strap by a PO (Bryan or earlier) any ideas anyone?