With the popularity of these motors, past and present, why doesn't anyone market headers for them? Maybe a nice set of well designed, tightly tucked shorties. Sure, you can find some for the early motors, even the early 371s. And yes, flanges are available, but you need time and skill to make a nice set of headers.
One issue is the changing exhaust bolt pattern. While I understand the popularity here, if you were a header mfr, the actual market would be very low. Just be glad we can get flanges.
They are popular with precious few of us on this board, and I am sure that once you get out into the 1-800 HOT ROD world that the market is nearly non-existent. Aside from the difference in model years for the head/port design that may be one reason.
I had a set of iron Fentons for a '49-'53 303'' that had been hogged out for 394 ports. It ruined them unless someone had the patience to repair the damage.
Just not enough demand for a company to tool up to make them. Most of those motors were used in full size Oldsmobiles, so no one wanted headers for those cars. Years ago I found a funky set of home built lakes headers for a 394 on Ebay and bought them. As crude as they are, someone did a pretty good job back in the day. They are made from early Ford torque tubes and a set of flanges. Gonna clean them up, do a few things to them, and run them on my rpu with the 394. Don
I used the exhaust gasket as a template and cut out flanges. Had a HAMBer make up the lake pipes. They look fantastic.
Here some early Fentons with Siamese centre ports, they weren't cheap when they sold on E-Bay either.