hi im building a book chassis and fitting 4 point belts the book shows you welding a triangle bit of 3mm plate on the inside of the trailing arm bracket. is there still going to be room for my seat belt mounting ? do you use the same hole as the trailing arm ? a pick would help if any on could show me there bottom seat belt mountings thanks

Some people just use the same bolt for both.

and is it ok si for the sva thanks

As long as it's a big/strong enough bolt, then yup. Something in a 10.9 or 12.9 should do fine if you're not sure.