I agree the 300 six is the best engine Ford ever built. There are ones that have more horsepower, and ones that have more torque, but if you want good torque, good horsepower, and longevity, the 300 six is the way to go. I just bought a 66 shorty F100 with a 240. It hasn't ran since the late 90's and I got it running in 2 hours. It may not last long, but I will just replace it with a 300. The 240 is a direct swap for a 300. I have even toyed with building my own combo of the 2. Use the crank and rods from a 240, and the pistons from a 300. It would make a 329, and a torque monster.

On the subject of mileage I have spoken to people who claim they get up to 20 mpg from 240s and 300s.

It took me 6 months to find mine. Decide the things you will not sacrifice, and wait for your truck to pop up. I found mine within 3 miles of my home.