1975 Duster front seat belt bolt locations?

Are you talk front or rear seat belts?

The rear belts bolt under the seat bottom. Push it and lift up, then you should see the bolts or at least the holes to bolt them down.

The fronts we need to know if you have a single retractor or a double.

Riddler

The front belts, and they have double retractors. Combined lap and shoulder belt.