I just completed a cross-country jaunt in my '48 pickup with the flathead V8. Trip went from nw Montana to eastern Ohio by way of Denver, Wichita and Kalamazoo, MI. The return trip was a little more direct. Total miles logged was 5,391 and averaged 15.7 mpg eastbound and 13.5 westbound (headwind). Used a quart of oil every 350 miles or so, and I dumped in a can of lead substitute every other tank.
Only significant problem was loss of one waterpump in central IL requiring overnight air shipment of a new one from Sacramento Vintage Ford.
Smoothest running engine I've ever driven across this great country.
Get those flatheads out and drive them!!