That louvered rear valence must be a truely rare item. I remember the /6 that Pat was referring to previously, and the slotted rear panel was really cool looking. At the time, the mid '70s, not a lot of concern and attention was paid to originality. That 914/6 with the slotted rear valence was certainly unique and those of us who noticed it knew it for a "custom" piece of fabrication, but I don't think neither Pat nor I had any idea that such a part was (in theory) available as a factory PORSCHE part.
Besides looking great, I'd bet the slots in the deep valence panel would help relieve the hot air build-up beneath the engine and by the muffler.
I would imagine a reproduction, slotted, rear valence panel would have a limited market, given that it probably would be expensive to manufacture.
Paul