From what you've said you want to do with the truck I'd say forget the headers. Good headers that don't leak and need retightened frequently are expensive. I have L&L's, which do have a nice thick flange, but had to notch the fame to make them fit.
I love using headers and usually do but I also do custom exhaust all the way out. I have not used long tubes on a truck for years simply due to fitment issues and 4wd makes that even harder. I use short headers as a compromise and route the driver side under to the passenger side just as ford does. only not into a y pipe normally. I do have one that is twin primaries from the headers as 2 1/2 going into a y to a single 3" all the way out. ford does this to avoid all driveline issues and front fuel tank and it's very hard to do better. all that said, it is really unnecessary for the masses. how the truck will be used normally is most important and for most the manifold is not only good enough but often better when you consider heat, noise, and repeated bad gaskets. good headers are not cheap and cheap headers are not good
To show that I am a caring and benevolent guy...I had my youngest son under the truck. He asked for a headrest....so I gave him a 4x4 piece of wood. I am so giving it hurts. 🤣
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.