I would like to know where I can order this (in Belgium maybe
)?
That's an EMPI 3894 "Show Bar."
I had one in my '66. I don't know if I would trust it as a protective device but it is wonderful if you want to bang your head into a giant tube all the time. The thing is more likely to hurt you than protect you in a collision. And for the front seats to go back fully the seat backs would have to bend. At least it was that way on my car.
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Find a shop to build a proper weld-in cage. You can do a lot better than that for a lot less money than just the shipping overseas.