I highly recommend using Raven's 7.6 distro. It has been patched to 3.1 and has the newest Sentinel installed already.

can I just install that over my 6.5 and run the upgrade scripts?

I don't think you can upgrade directly to anything other than 6.6 from 6.5. If you want to install a new version of nuke then it will have to be a clean install I believe.

There unfortunately aren't upgrade scripts for that distro. If you want to be as secure as possible, and retain your current site, upload 7.6 and run the upgrade scripts in order (6.5-6.6, 6.6-6.7, etc up to 7.6), install the 3.1 patches from chatserv, and then install Sentinel.

As always, please backup everything beforehand. Feel free to ask if you need anymore assistance along the way.