EBS - Is that last set in your stash from Nicson? They look like pictures I've seen of them, but don't see the name anywhere.
They're Clark headers. They're stamped sheetmetal welded up at the seams.
Clark headersClark AdvertisementThere is also a type, I assume made by the same Clark company that are cast iron and have the name in raised lettering. I've only seen one or two pictures of them. I've seen a couple sets of the sheetmetal type in person, including the one I own. I've never seen any on a car nowadays, though I've seen vintage pictures of them in use.
A company called Smith-Reisor also made a similar set that had manifold heat. I saw a set for sale on Instagram a few years ago, misidentified as Clarks.
Smith-Reisor AdvertisementSmith-Reisor blurb Hot Rod Magazine Jan 1954Here are what Nicsons look like. I *think* Nicson only made them for GMC.
https://oldchevytrucks.com/blog/2014/02/fenton-vs-nicson-headers/
