Two Start-up Disks

I am planing to install OS10.8.5 on a new internal disc on my MacPro

and use it to keep a version of PT10.3.9

Would it be better to uninstall/delete PT from the other disc before updating it to Mavericks? What would happen if I don't?

I still want to use my Mbox3 with Mavericks

Thanks,

Wolf