What mileage does your slant six powered ride get?

About 15 years ago my mom came up from Mississippi in her 73 slant dart. It wasn't running well to I tuned it up for her. Don't remember where I set the timing but I rebuilt the carb, put on new wires and plugs. On her way back home she swears she got 32 mpg. These were all highway miles and she never drove over 50mph. She was a nightmare on the interstate. I guess its possible.