There are dozens of different ways to mount of pull up bar. It's a project that's really unique to your situation so there's no way to give a design that everyone can use. That's why I haven't done a project for it yet even though it's a very important piece of lifting equipment. But I finally decided to just shoot a quick video showing you what I did to install a pull up bar in my home gym.
The most well known commercial neck harness costs around $40. For what amounts to a few straps and carabiners that's quite a lot. I decided to try to make my own. I did it for less than $10. I use it mostly for strengthening the muscles to reinforce proper posture. There is another DIY design out there but I decided to try to make mine look a little more professional.