I bought a '77 K20 last weekend that is bone stock with 73,000 miles on it. It has a 4v350/t350/205 combo with 7.50/16's and Im betting 4:56's 'cause I filled it up and went just over 100 miles before it was empty and it's wound up pretty tight at 50 mph. It's got the option sticker in the glove box, but there's no reference to axle ratio. I don't know what size tank is under it but I'm guessing around 16 gallons. This thing runs great, you don't even have to touch the gas pedal to start it unless it sits overnight.