I have a 1986 3.2 and was in the same dilemma. However I learned that either in 85 or 86 and later the three point seat belt retractor mounting holes were factory installed for either Sweden or Switzerland market (cannot recall exactly) that requiried 3 point belts. Indeed they are there. So I fabricated this tether bar for use with a child seat and will use the lap belt configuration with tether. Once the car is put together, after some other mods being done, I plan on going to buy buy baby and sampling various seats for fitment. More to come on that in the coming weeks.
Regarding crash worthiness, entire system is fabricated using 1/8 sq bar and 1/4 plate and class 10 bolts and nuts. It is heavy and stout.
Once my child is old enough for a booster with lap belt the 964 3 point seat belts I obtained will be installed. The holes currently in the parcel shelf have been cut to receive the belts and fascia ring. So it's a fully modular set up.
If one does not have the parcel shelf belt retactor factory fastening mounts I do not encourage using any set up where drilling holes and installing bolts in the BIW body parcel deck, unless proper reinforcement is provided.
