I bought a set of front seat belts for my 1972 911T from PE Parts a few years ago:
Porsche Front Seat Belts | Professionally Engineered Products peparts.com
The new belts are retractable and do a great job. They took less than an hour to install. Highly recommended.
The only issue is that the receptors do not appear the same as the original belts. The safety element is worth the non-stock look in my opinion. I sold my original retractable belts for half what they are worth today. I recommend that you keep yours in a box or at least sell them for today's market value.