G'day and welcome.
What state are you in? Geographically speaking.
Basically you can't install seat belts yourself where you need to add mounting points.
Bizarre ·
Aussieveedubbers · ICE and Interior Forum
https://forums.aussieveedubbers.com/threads/112343/61-beetle-interior-questions
Bizarre ·
HappyDaze ·
Emmett61bug ·