Who made these headers?

Perhaps one of the gurus can help ID these headers. They came on the 340 in my 69 Dart. I can't find a maker's tag or mark anywhere. Color-wise they appear to be made of stainless, but they have a lot of surface rust on them. I've not seen the slotted bolt holes on a header flange before.

DSCN0064.JPG DSCN0065.JPG DSCN0066.JPG DSCN0067.JPG