Rear seatbelts 64-66 barracuda

Anyone put retractable 3 point seatbelts in there cars? Rear seat to be exact. Fronts are easy. I have small kids and need to do this. If no one has i guess I'll be the first..

I also haul kids around in my '69 Barracuda and went through a lot of trouble to make it safe for the kids. I have a non-fold down rear seat and I know the 64-66 aren't quite the same but if you want to see want I did to solve this problem just ask me to post pics here and I'll do it.
PS- I also made a built-in rear headrest for the same reasons.
treblig