Cuteo,
Sorry if I sidetracked your concern. Something is better than nothing, and the better design and fabrication you do will certainly offer some safety. I think like most convertible drivers, many of us have simply accepted the risks of old vehicles rather than go through a long process to lessen, but not eliminate, the danger.
When you look at modern race cars and their roll cage designs and see drivers escape unscathed after a horrible crash, the value of a cage is definitely there. But short of a ground-up engineered and fabbed comprehensive complete design that would be highly awkward as an everyday driver, even a modern automobile with door side guards, standard seat belting, and multiple airbags cannot promise that level of protection for a driver or a family. And still without a race car head restraint, 5-point quick release belt, fireproof suit, onboard fire supression system, and an on-track rescue group at the ready, surviving intact from an accident situation is still a matter of luck.
As the world approaches driver-less cars, it will be interesting to see how the designs and regulations attempt to protect unbelted unaware passengers from the hazards of future travelling.
Good luck with your project; you have my support for what it's worth. Look forward to see what you come up with and will be envious of your results.