What mileage does your slant six powered ride get?

Damn! I only just threw out all my calculations the other day, we had done a long trip, I recorded all the details... 1964 Dart GT, stock 225, automatic, 2.93 diff gears, 2 1/4" exhaust, 225/60/14 tyres.
The end result over about 350 miles of highway/country roads driving was average about 23.1mpg (19.68L/100km). Note: that's using real-deal UK Gallons, not "Diet Gallons" HaHaHa!