I spoke with a gent at a car show today that had a 5.0/ auto OD in his 56 today. Very clean and nice looking install, and he said he gets 23-24mpg! If a killer deal came up on something like that, I might like to do the same. I'm still a little afraid of EFI installs though... never done one.

300
The 300 cu in (4.9 L) six was added for the F-series in 1965. It was essentially a 240 cu in (3.9 L) with a longer stroke. The two engines are nearly identical; the differences are in block dimensions, combustion chamber size, and the rotating assembly. It produced 170 hp (127 kW) (gross). The 300 became the base F-series engine in 1978 at 114 hp (85 kW) (hp number changes due to Ford switching to net power ratings in 1971). Power outputs were increased to roughly 122 hp (91 kW) during the early 1980s, before fuel injection was introduced. This became the primary engine of the line, eclipsing the 240. Unlike the Falcon engine, it featured separate intake and exhaust manifolds, which could be easily replaced with aftermarket manifolds offering the promise of even more power, through the installation of larger carburetors and a higher flowing exhaust system.
Also during the late sixties and early seventies, the 300 was used in larger vehicles such as dump trucks, many weighing into the 15,000–20,000 pound (7,000–9,000 kg) range. These 300s were equipped with a higher flow HD (Heavy Duty) exhaust manifold, since the engines were going to be constantly working in the 3000–4000 rpm range. These rare, yet effective, manifolds had higher flow than the electronic fuel injection 4.9 (300) manifolds and some headers.
Engine sizes were converted to metric for 1983, causing the 300 to become the "4.9". Fuel injection and other changes in 1987 pushed output up to 165 hp (123 kW) with 8.8:1 compression. This engine was gradually phased out, ending production in 1996, and was replaced by the Essex V6 in the F-series trucks with their 1997 redesign. However, it was renowned for its durability, low end torque, and ease of service. The 300 4.9 came with the Ford C6 and E4OD transmissions, as well as the Mazda built M5OD 5 speed manual transmission. The 4.9 liter 6 cylinder was built in the Cleveland, Ohio engine plant.
This engine is also used by Stewart and Stevenson in the MA Baggage Tow Tractor (pdf), and Harlan in their standard tow tractors [1], as well as a multitude of other pieces of equipment, such as ski lifts, power generators, wood chippers, tractors, and, until they converted to diesel engines, most UPS trucks. Many UPS trucks still use the 300 to this day.
In stationary service (generators and pumps) fueled with LPG or natural gas, this engine is known as the CSG-649.