Interesting ...
We used to spend some time sharing the roads with the Appalachian rustics when we would shake our heads and say, "Drove inter town 20 mile an hour; Don't keer if Ah do get kilt!"
Well, you could come around a curve in your Volvo doing 60 on State Road 622, say, to find an ancient Chevy pickup with a load of chickens in the back doing a steady 20 down the middle of the road while making rough track corrections every now and then. As you squeezed past you caught a glimpse of Granpaw in there gripping the wheel with hands white with stress at this high-speed trip to town to rub elbows with strange folks who wore shoes even in summer.
With the hillbillies it was "mile" and "foot" and that must have been correct a long time ago.
Even today you might have a 20-foot trailer that is 20 feet long. That is standard English. Granpaw would say it is 20 foot long.