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Seriously, no welding is required with the Motive systems, unless you are going "show-correct", eliminating clamps.
I've always found welding to be more reliable, though. Less likely to leak, or let the connection come loose or develop a hinge like the U-bolt kind always seem to end up doing. Maybe the band type of clamps like on the new Mustangs are better?
Either way, I would not approach this kind of job convinced that everything is going to fit as accurately as dropping a new intake manifold on the engine, and that you'll absolutely be able to just tighten a few bolts and be done with it. Exhaust systems aren't that accurate, and clearances can change over the years.
I think you should find a good shop to do it so when its done you can see that the trumpets are straight. The kit that was used on my car we had to put a pipe in the tail pipe and bend it straight so the trumpets would line up right. And they still didnt.