Where to buy Seat belts front and rear for Mk 1. Aftermarket ok.
 
tried a few places, to no availability.
 
Seems all originals been used up by GT falcon boys?, The car I own  owner sold them to GT resto guy.

I got Klippans from Autopro.  Had to be ordered in but didnt take long.
 
There is also http://www.apvsafetyproducts.com/seat-belt-replacement-guide

Looks like a good solution,
It would be worth a check however when fitting the centre rear seat belt nominated within the kit. A Mk 1 Capri is plated as a 4 seater, so installation of centre belt if so inclined may require a mod plate or similar to be fitted.

Ah, not ALL capris were 4 seaters, believe it or not some plates say 5

gtv6capri is right in that, although the great majority of Capri's show seating capacity for 4 only people, some do have a 5 stamped on them!
 
ADR 4 (Seat Belts) states that only front seat belts need to be fitted to Capri's built in 1969 and 1970. However, from 1 January 1971, ADR 5A (Seat Belt Anchor Points) stated manufacturers also had to include anchor points for rear seat belts. BE AWARE that Ford stated fitting rear seat anchor points from as early as February 1970 and so therefore you should fit rear seat belts wherever there are rear anchor points available! On the Capri ID plate it states which ADRs the vehicle complies with, so if it says 4 and 5A then you should fit seat belts to ALL seats, that is, at least 4, if not 5 seats.