Must mount 6 point belt in Panteran. Has mounted a cage. How have you done?
Install a horizontal bar within the roll cage as suggested or use the harness bar available from vendors, however if using that in a racing application I would add fastening bolts through the firewall toward the inside of the seat at either side of the engine access hatch. The existing sill mount should be strong enough for the lap belt, you may need to strengthen the inner floor mount point. I would mount the submarine belts to the rear seat mounting points or the same as the lap belt.
Of course it is always wise to check with the sanctioning body you will run with as to what is acceptable and regulated.