Oooorrrrrr
Someone is embellishing.
It's the whole combo that makes or breaks it. On the cars you listed you had a 440 (no chance), two cars with 3.55 gears, and a 4x4. None of those are set up for mileage.
If you have a small block, shallow gears, AND Overdrive, plus a bit of tuning, it's within reason.
I drove my Aspen 1500 miles once a month, so I was very concious of my mileage. It is possible. As I set up my Challenger, I'll be swapping to an A-500 with lockup, getting rid of engine driven fan, putting on a nine flowing exhaust, and some taller tires. We'll see how it comes out.
At almost $3 a gallon in AZ, I don't need high performance, I want to be able to afford to drive it everywhere.
Besides... When you look this good, you don't have to be fast!
bill