The trick I was shown is to put a penny in between the gears and it will pretty much hold everything in place while loosening that nut up and not harm any gears in the process since the penny is relatively soft. It works well for putting everything back together again also, but not nearly as needed since that nut isn't dimpled yet to hold it in place. But I have an electric impact wrench now and it makes that job super simple and quick. The 350x has the same basic clutch set up.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90