My Long Tube header build

[xnamerxx]

Flux core welds look like crap but you should be able to weld SS with it as long as you have the correct filler.

There's also quite a bit more that needs to be considered with header design, just welding longer tubes can actually result in power loss if it calls into a dead range where the reverse shockwave happens too quickly or too slowly. There are other things to consider in regards to load and heat and such but that would quite a bit of time to type out.