Seat Belt Regulations

While I'm guessing that you "ain't from Texas" how would anyone answer the question without knowing where in the world you are?

Why not just specify what you want?
Exceeding a standard/requirement isn't going to be a problem.
Del

Who ever is building this for you is doing to want to get paid. Are you the authority that is paying for this, or is there some other funding for it? Whoever is paying for the vehicle has the right to specify whatever they want in their vehicle.

The FAA in the US commonly pays for the fire equipment that they mandate. They set the minimum standard. We get to upgrade, change, or move equipment as long as it is justifiable to the FAA. Commonly departments will order brightly colored seat belt assemblies so as to make it more visible to outsiders looking in the truck.

If you want 4 point restraints, say so in your spec. All the manufacturer can do is charge you for them, or try to explain why you can not have them. Good luck.