Seat belt options.

[Copilot]

Has anyone used the seat belts in the link, or something similar? maybe from a 70's Dart? I do not want to use the original belt that attaches to the headliner clip thingy.
3-Point Retractable Lap & Shoulder Seat Belts

 

[pschlosser]

When choosing aftermarket, and seeking a three-point system, I've used these in a couple of builds. They are well received and look much like the ones you linked.
Retractable Seat Belts 3 Point and Lap Belt Replacement

 

[heminut]

I used the aftermarket ones similar to what pschlosser posted in my Cuda. I welded a tab inside the rear side panels and mounted the retractor there out of sight with the shoulder belt coming up through the hole in the rear panel where the little ash try was. I definitely suggest you get the belts with the longest drop sash guide you can find to keep the shoulder belt from riding your neck when you use them.