I'm not disagreeing with you necessarily, but it is worth looking into. I mean what other car gets welded like that? You don't weld a Miata up solid for example, right....? It would seem reasonable to assume the cage is the safety devise and car should crumble around it. And considering the 914's are an already fully welded car (as apposed to bolt on panels etc...) I would think a car in structurally good shape should be plenty strong without welding solid and creating a brick.
My thoughts (disclaimer, I am no expert, just my opinions
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