Note the casting numbers at the top of these two OEM housings, they are not very well defined https://pbase.com/image/154153755 in the Magnesium casting, as most other Porsche factory race parts I've seen. These two early Magnesium Fan Housings are now approximately 44 years old. Very rare and cool race parts.

About the difference in color. I lightly media-blasted the light gray colored fan housing and sprayed it with ZepPreserve (great stuff!). The darker fan housing will get the same treatment, but only after a small ding repair https://pbase.com/9146gt/image/154153736 at the edge of the outer ring, the natural darker Magnesium color will return over time.