Thanks Tim, This is what I have done
As you say the replacement driver these days is the 300R which the same for the 580/600/650, I understand the damping materials have been updated in time so sound would probably differ but hopefully improved. If you check replacement grills they also now the same for all 3 models as guess the plastic grill from the 580 no longer available.
So I have order from Sennheiser uk .......
Grill replacement (092815) 2 x £10.24 £20.47
Foam disc (049789) 2 x £0.41 £0.82
Cable straight with 6.35mm stereo jack plug (3m) (092885) 1 x £11.27 £11.27
Dynamic neodymium capsule (300R) (092855) 2 x £37.87 £75.74
So I get the lot for £112 including delivery.
Now as a new pair of 650s still going at around £300 on amazon that seems to make sense
I can then 'play' as much as I want.
I can try 580 lead versus 650 lead
580 grill versus 650 grill
and if I decide for any reason I prefer the sound of the older drivers (which sure I wont) I will take the new spring clips from the connectors and fit them to my old 580.
More than I had intended but sounds like a fun project to amuse myself with.