Factory produced 440 "M" code Darts & Barracudas were '69 only. For years, 640 Darts has been the accepted no. At Carlisle in '04 they were the featured cars and 2 guys from up East had set up a registry and held a seminar, during which, they said that by comparing production dates and sequence nos. of a quantity of cars built at Hamtramck they thought the no. was more like 350. As scarce as they are today, they might be right. There were 7 production dates so they were built in batches of who knows how many each.
The cars were spec-ed out as 383 GTS hdtps, partially assembled, then taken to Hurst's
facility on E11 Mile Road in Madison Heights for for final assembly, including the 440 engine installation. They were all TFlites with SGs and your choice of 3.55 or 3.91 gears.
Right side exhaust manifold is identical to all the 383 cars, while the left side is unique to that application. They were all built with manual drum brakes and manual steering. The bodies were unaltered, and all came with bucket seats and consoles. Magazine test results were always bogus, because the cars the magazine guys got hold of had all been "tuned up". All the manufacturers did it, not just Chrysler, because after all, their
primary concern was selling cars. Period. I Hope this has been helpful.