Currently, I have standard lap belts purchased from one of the popular sites. After reading about Mickey's misfortune, I'm considering something better. But I agree with Tim, that 'B"pillar is not what it is in modern vehicles that are engineered to take impact and provide a mounting point for a safety belt.
I remember a post not that long ago showing a flipped wagon somewhere in CA. Most of us were commenting on the conversion and the issues facing SOA's.But I do believe that post mentioned that the drivers were pretty beat up.
Fact is, even with the springs under the axles we're still driving vehicles with suspension derived from horse drawn wagons. ATC, driving an old Willys wagon or truck on modern highways is akin to riding a motorcyle on the street. And a little ol' CJ with a rag top? For me, going out in the wagon is like drawing straws, I just hope there are lots of long ones in the bundle. And it's not only getting hurt but messing up an old car that is hard to repair and I've got lots of B,S, n' T's into; but I digress...
In my mind I see a stylie roll bar fab'd from oval tubing and made to fit as close to the "B" pillar as possible. It bolts to the floor with braces underneath that attach to the frame. Not only does it provide 3 point mounting for the front seats but the rear as well if it has aft bracing. And it just might help keep that tin roof from oil canning on your cabeza!
But I'm no engineer so don't even ask. Plenty of folks on this forum that could chime in with real world designs.
Of course all of this begs the question: When is Mickey gonna post up a mug shot?