Where do you buy your exhaust?

OK Ill actually answer your question.
ANY reputable exhaust/muffler shop can and will build you an exhaust system from the manifold back using 2 1/4 pipe. If you can tell them where it was routed it will help and they would love to have the flange that attaches to the exhaust manifold (or headers if you are going that route). I know of 0 (none) stock exhaust bolt on systems for a slant 6 powered car or truck at this point. (possible exceptions of NOS or REALLY pricey repops) Mine as recently as 1 month ago cost about $200 for a slant 6 truck for the full length exhaust and turbo muffler.
Frank