How rare is this car?

Nice find!!! Don't see to many 2nd gen Darts with the 273 Charger engine (273 Commando was the Plymouths name) as its a one year only body-engine combo. '67 Was also the last year for the HP 273. Also with the rear axle, V8 cars equipped with a manuel trans got the 8 3/4 starting in '66. All 340, 383, 440 cars got the 8 3/4 too. This is not to say that /6 (both manuel & auto) and 273/318 cars cars (with auto) couldn't have gotten the heavy duty rear also as Mopar was like that.