I believe the brow piece is chrome plated on the BJ7 and BJ8. I have an original which just happens to be sitting here in my office and it looks just like the oval surround in finish and magnetism (stainless steel is usually non-magnetic). It's even painted silver on the back like the rest of the chrome. My bet is that the chrome has just gotten thin from all the polishing and exposure over the years and the fine scratches have that S.S. look.
BTW, the vertical bars should be anodized aluminum, not chrome (see many Healeys refinished incorrectly in this area) and the inner oval surface of the chrome surround is painted with flat silver paint after chroming to reduce the reflection of the vertical bars into the surround.
Cheers,
John