I had some concerns about the strength of the seat belt mounts in my Classic Revival.
There's a folded lazer cut steel plate that forms the seat belt and one of the roll bar mounts.
I strengthened it by adding a welding a 3mm thick shear plate accross tha back of it. You can see the shear plate with the round holes to lighten it in this pic. It didn't add a lot of weight but it sure strengthened up the whole thing.
If it's for safety and things like seat belt mounts it's better to over engineer in my opinion.
Cheers