Cost/benefit might not be good, but knowing things are better counts for something. Use the 1972 IMPERIAL muffler and match the pipe sizes on it. Same low restriction as the Street Hemi muffler, but C-body quiet and size. When it comes time for the lh side, then duplicate the right side (mirror of the rh side on the lh side) and get the lead pipes built.
I got the '72 Imperial pipe (ball joint connector to muffler), muffler, rear pipe (over the axle), and "resonator replacement" pipe. All from Walter Exhaust, so it fit as it should have. Due to the pitted condition of the balljoint on the y-pipe, I needed to do some additional work there. Easy, painless, and nice. Never did get any baseline figures, but I know it's what I term "sewer pipe single" exhaust. Correct for the vehicle. Due to the rear quarter panel rear area differences, I had to get a muffler shop to bend the very rear pipe upward to clear the trailer hitch. No big deal.
ONE thing I like about the OEM supplier replacement parts is that the pipes and mufflers do tend to last much longer than any muffler shop items I've ever had. Looks right, hangs right and reliably, and lasts. Otherwise, some high heat black or silver paint before installation.
On the '67 Chrysler ONLY, the 383 4bbl had single exhaust. Plymouths and Dodges had duals for the same engine. 325 horsepower ratings for all.
CBODY67
