Well, in my book, if I get T-Boned in my 1970, I will look like nothing usefull! Have a look in those doors. The S30 is a thin can, with the engine coming right beside the 2 occupant in a front collision crash.
With all that said, I personally would run a cage, maybe not a full one but at least with the sidebars (6 point). I have the same goal as you in mind and I will run a full cage.
At the end of the day, they say that in an accident, what you can touch with your hand, you can/will hit it with your head at the time of impact.
I am subscribing to this thread for sure,
Dayz