If you can't find the instructions that came with your seat belts, contact the manufacturer, who will provide instructions. Never attach seat belts to race car sheet metal, including the floorboards. Never use passenger car seat belts in any race car, including an Enduro. If you're racing, you're likely to crash. The added time and money required to install a good 3-inch lap belt and shoulder harness are worth it.
People die on quarter mile tracks.
This mounting tab is badly welded. The gathered dust shows the weld has little penetration, and much less strength than it should. Click photo to enlarge 3. If you're a beginning welder, find someone who welds for a living to attach your seat belt tabs and the mounting bracketry for your seat. If you're a beginner, find a pro to weld up your roll cage, too.