It can't have been 60s or 70s.. it was an X reg. That puts it firmly in the 80s.
I'm not a fan of doing stuff like that on Top Gear at all. It's cheap TV, to me. I can't help thinking that the fact that the show has a big budget because it has a big revenue is sometimes resulting in ever more cheapening of the format itself. The BBC has a responsibility to the licence payer, first and foremost, and crap like that isn't meeting that responsibility. And I don't even like Porsches.