I recently went to a local muffler shop to inquire about a 2-1/2 inch exhaust system. They said they could only replace it from where the two collector tubes connect back -- no so good since this is currently about a 1-1/2 inch pipe. They said I would have to purchase the collector pipe elsewhere.

Where can I get the piece that goes from the stock manifold to a 2-1/2 inch collector?

If I buy the kit from MSA, does this include pipe from the manifold or just the collector?

If you swap in an exhaust manifold from a 280, you'll get freer exhaust flow from the manifold itself - and the not-quite 2" collector (the Y-shaped short twin pipes that go into one single 2" pipe) - or down pipe.

Or, any good exhaust shop ought to be able to cut/weld the stock flange from the exhaust and build you a 2" downpipe.