And Porsche homologated these with the FIA why????
The only reason that I could think of would be to make the 911"T" eligible in the 4-seater touring classes back in the late 60's and early 70's. But if that was the case, why bother at all, just use the stock units unless these are a lot lighter. Are you sure that they are not some sort of aftermarket pieces created for some long forgotton reason? Given the limited headroom (and leg room) in the back, I don't know why anyone would buy these over the standard units.
A mystery wrapped in a riddle....