Fuel Mileage question

[77 Beater]

I have a chance to get a 1986 chevy 1/2 ton for a really good price. The engine has more blowby than I like but has about 150 psi on every cylinder and very good oil pressure. When I looked at it I was stunned to find the engine is still all original and very responsive. Nothing has been altered. Owner says say it gets about 9MPG but I'm thinking its capable of more like 15-16 mpg. It has a 305/700-r4/208np and either 4.11 or 3.73 gears. I'm thinking 3.73 was more common but not sure. Anyway, what do you guys think this truck is capable of as far as fuel economy goes?

[1980c10]

My 82 1/2 ton lwb, 305, Q-jet, 4 speed manual, 4x4 with 31" tires would always get me about 18mpg in town or highway. 15-16 is realistic after some tune-up carb rebuild or whatever it needs.

[1984k30]

In half ton 80's trucks I think 273 or 308 gears are more common than 373.  9mpg seems low but depends on driving style.   Light footed you should be able to get at least 13.  If you live in  Iowa you may get 18  but if you live in a hilly region I would be happy with 15.