I installed the front and rear 4th gen seatbelts and entire interior about 4 years ago. Made all my own brackets too. One of the first very people to do this complete conversion. Everything still works to this day. Those morrisclassicconcepts seat belts look pretty good too and if they are a direct bolt in thats probably your best bet.
Here are a couple pics of the interior in my 69 Camaro called ILLUSION.
