1970 Duster odd vinyl roof option

I have seen those tops back in the day here in SoCal especially on the 73 to 76,77 ply. Dusters. Not to say they were not in other states. I asked about the top back then at a dealership I was told it was a factory add on. I believe they said they referred to it as a "halo top" stands to reason it looks like a halo.