M code barracuda

Well since that wasn't a body in white, special order race car if you imagine the warranty issues if they would have stuck a 4-speed in those bad boys? Brutal! Now I've talked to a couple people that actually own original numbers matching ones, what I can't figure out is where the 383s and 440 cars, (H and M) built to Magnum specs Factory?
I think (think!) they were magnum motors, but were down-rated because of the terrible drivers side exhaust manifolds (the 440 manifolds are worth a fortune, cause they were thrown away for headers.)
Edit: tree'd by Hemi Dart!