The mufflers and resonators are new tooling with unique part numbers. Single exhaust transverse mufflers have always been dimensionally challenged compared to the originals. About 4-5 years ago (I've lost track) Imco, who was the main supplier of mufflers to the aftermarket, decided they were getting out of the muffler business. Every exhaust supplier went scrambling for new sources. Keep in mind that mufflers for older cars are a curiosity for these suppliers who make mufflers for the main stream replacement market. The new sources were just as dimensionally challenged as Imco and they did not make the resonator. We contracted with a manufacturer for mufflers and resonators that were correctly shaped and dimensionally correct. They are a lot more expensive than the standard mufflers supplied in the current repro exhaust kits and since they are dimensionally different we had to make separate pipes available to match. The single exhaust transverse muffler for 65-66 & 67 are $200 and the resonators are $150. These are extremely low production parts. We now have correct mufflers for 65-66 & 70 inline and 67-69 transverse dual exhaust cars as well. The mufflers started arriving into stock in January and now that I have both the single exhaust muffler and resonator I can send them to the pipe supplier to create fixtures for bending the matching pipes.
The change in the new MCA rules has put a flame under me to get these things done.