So I bought a project mk3 supra here's how the buckets are mounted .So the bolt is going through the steel box section through the floor where it's bolted .
Photo is massive I'm not sure how to change it sorry
I assume the box section is braced on something out of the picture and it's not just flapping around? For example a raised piece of floor that it is bolted down tight to? Safety depends on how the load is spread top and bottom where the nut/bolt head sits, if it's like the top and the only load spreading is through the seat fabric that isn't ideal! To give you an idea harness eye bolt spreader plates are 2 inch square. I'd sack it all off personally and start a fresh doing it properly.