welding coated headers

I was planning on dressing the headers before I have them welded, but I was more worried about the section around it heating up and burning off the coating

its not to put in any O2 bungs, just fixing some scratches

(on a side note, which way SHOULD the castlenuts point on the 71 steering linkage, up or down?)

and where would one purchase a can of ceramic coat spray?

Did you mean ADDRESSING them, or dressing them? If you're thinking of exhaust wrap, don't. It's probably not in the ceramic coaters' fine print and not widely known, but that's one of the major reasons they can deny any warranty they might have extended to you when you bought them. If they suffer real versus cosmetic damage at any point in the future, I suspect any touch-ups with Eastwood products would also void it outright.