Many thanks to all that’s put this thread togther and those that have helped me through the ‘upgrade’ to CM3+. Great community. Now up and running and delighted. I’m new to both Mac and Raspberry (ok I know it’s obvious 
- but getting there slowly)
A couple of things that might help others that tread this path …
I used a 10mm 1/4 inch drive socket that fitted exactly - so real easy to undo /redo the encoder nuts
Also not being familiar with the run/disk mode switch - 'twas obvious once inside the norns
finally a tip - the encoders are a rubber knob and easily pull off. Note when putting on they need to align up with the shaft. Also the buttons should come off as makes disassembly easier.