jb weld will break down over time under high temps. most exhaust shops can do it for you, heck if your worried about how it will look just ask before its finished up if you can see exactly how its going to look and if they will work with out
if you decide not to have it welded you can use exhaust clamps/exhausts tap and such and put it together yourself without welding (maybe jb to get everything in place)
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