How to maximize gas mileage with 1969 Mustang with 200 inline 6?

[fortuna 10]

Hello guys, new member here. I recently got a 1969 Ford Mustang coupe with a 200 inline 6 engine and 3 speed manual transmission. It's in great condition, has had regular maintenance and has just recently had a tuneup/oilchange. However, everything is stock on it with no modifications and currently I am getting around 12-18mpg with a mix of city and highway driving.

 

I would really like to make this my daily driver now and am prepared to invest money to make this happen. What can I do to improve gas mileage and make this more practical to drive daily? I would prefer to do this without swapping out a new engine or transmission.

[Max Power 74]

Well, the transmission is the big thing. The three speed is really inefficient in it's gear ratios, or lack of them. Carb in good working order, synthetic fluids, a Pertronix Ignitor instead of your points, efficient and properly inflated tires would be a couple of other considerations.