This guide is six years old which actually makes a difference here - the OS, gpsd, and ntpd, have all changed considerably and much of the software configuration instructions are now wrong.

The general concept still works fine but you will have to research more up-to-date documentation.

These are my notes from the last time I did it, which are pretty scratchy, but hopefully you can glean something useful from them:

https://pastebin.com/f4N2NSQB