Thanks, just 'won' it (the MBP) on eBay, so hopefully its a good one. Will test it before doing the swap.
I've done similar before, even put a bigger HDD in an iBook (nightmare) and it worked fine for years later.
One other question, I know the latest Mac OS works in even this old MBP, but what is the recommended Mac OS for a 2009 MBP 13"? I have Sierra and High Sierra on a bootable USB thumb drive, made them when I updated my iMac.
Going by the pictures this MBP has 10.8 Mountain Lion installed, can I upgrade online to the OS X of my choice?