The last time I contacted Safecraft in Concord Ca. They said that the restraint business had been sold or spun off. I contacted the new Safecraft Restraint co. in Florida(?) and the guy was nice enough but unfortunately didn't have the specs for the GT harness system that Safecraft Ca. Previously sold.
I went to their website. Very hard to navigate. A lot of nonsense and no real help; BUT the gal who designed it has her name all over it. I have the old restraint system (belts) charts on my laptop and will try to download later. I would suggest you go to the GT40 website run by Wally Rust (CobraR39?) becasue he had a nice set of belts and mounts ready to go.
Belts usually only good a max of 3 years; BUT, it depends on whom you are racing with whether they check dates or not. The belts are clearly dated on their labels.
Fia ratings are 5 years, and yes the tags are very clear, the brand I use, schroth, the tags say "not valid after xx 2016" vs the more traditional "date of manufacture". Other brands may have moved to the "not valid" labeling.