How rare is a 68 c10 w/396/TH400?

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I recently aquired a 1968 C10 short bed fleetside with 396 and TH400. Truck is all original with matching numbers and 73,000 miles. My dad bought it during the oil crunch of the 70's and we used it for our service station work truck. The owner was scared of the gas mileage at the time. He always said it was pretty rare, but I would like to know how rare. I can't find production numbers like you can for cars. If its rare, I don't want to customize it. If not, I want a blower sticking out the hood! Any help would be appreciated.