are 67 c20 dually's common?

[62k10&84k20burb]

My buddy has a 67 c20 dually, I know it has an sm420 4spd and a 350. According to the tag in the glovebox it originally had a 292 i-6. (Wish it still did) I'm unshure of the rear axle, anyways how common where these trucks? And. I'm not the best with older chevy rearends, so I'm gonna say a few things about it to help I.D. it. Its almost perfectly round & the inspection plate pops out in almost a perfect 1/2 ciricle. The plug is to the left
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[special-K]

C/20 cab & chassis with dual wheel option are far and few between. They fill a small gap between single rear C/20s and single rear C/30s. A single wheel C/30 is a heavier duty truck that a dual rear C/20. Does this truck have coil or leaf spring rear? Oddly,the only ones I can recall seeing had coil rear,which makes them all the more "oddball"

I think of dual wheel pickups when I see "Dually" since when GM first offered these in they called them the "Big Dooley". There were no Dually pickups from factory prior to '73.

[62k10&84k20burb]

Its a coil spring rear. Does anyone know about how many where produced?
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