Bolt in cage?

We were watching a "car Show" on Motortrend TV yesterday about prepping a Camaro for the strip.

Almost as an afterthought they installed a pre welded 4 point bolt in cage.
Guess that's Chevy life, just buy a premade thing...
Anyway, it made me wonder if anyone here has fabricated a 4 point cage and welded it outside the car and then fed it in thru the door/rolled down rear window and bolted it in with plates so as not to have to weld inside the car?

Dany's Magnum swap '66 Cuda is not fast enough to need it ( and probably won't be) and it is still a "street car" after all, but if we could add the extra margin of safety without gutting the car ( which is a pretty nice but unrestored car with most of it's original interior) I would be all for it!!'66 Barracuda.jpg