mid 80's 318 mpg economy numbers...

I have a 1988 Diplomat with 318, 122,000 miles since bought new. My average is about 19-20 mpg, all around. Made a trip, last spring, with a combination of 70-75 mph interstate, "normal" 2 lane 55-60 mph, and mountain roads with 30-35 mph. My average for the trip (approx 900 miles) was 23.7 mpg
I did remove the lean burn system, and used a earlier mechanical/vacuum distributer with a GM HEI system, and earlier 2bbl carb. 904 lockup trans, and 2.7x rear.