Cleaning/identifying a header

Well the studs are just 8x1.25 metric studs, ask the parts store for ford 5.4 manifold studs or just find a similar size. No real biggie to get out, just take your time.

The holes are nothing as well (yes I said holes, not hole) they can be filled with a few tacks from a MIG welder, it will probably spread a little, BUT you really didnt want that thin metal around the hole anyway.

I'll get some pictures posted tonight.

Now, the snapped exhaust stud, I can just unscrew it?

As long as you get a good grip on it, it will unscrew

What do you suggest gripping it with? Or should I just take it to a machine shop?

Soak it with some penetrating oil and let it sit a few days and keep it wet then you can unscrew the stud if there is anything sticking out.
On the pipes Oxalic acid is great, go buy one of those kiddie play pools, hard plastic type, then fill with warm water and maybe 1/4 cup of the stuff and mix around, as it turns green wipe it off with a scotch pad, just not too hard to scratch it. it's great to dip your chrome wheels in with tires on them, I used to restore old schwinn bikes and it's like magic how it works. You may need to just core out the baffle and get a new one to fit in there, it may be pretty rusted out. Worse case sand them down and get them ceramic coated.