Ford introduced the big 337 CID flathead V8 in 1948. It was available in Lincoln cars and Ford big trucks (F7 and F8) from 1948-1951. It was replaced for the 1952 model year by the 317 (Lincoln) and 279 (Ford trucks) Y-Block V8.
Speed parts and replacement parts for the 337 are hard to come by and can be expensive, due in part to its short production run and the fact that there is very little interchange between the 337 and the 221-255 CID flatheads. It is also a heavy engine at over 800 lbs, making it difficult to install in small cars. These factors meant the 337 never really caught on with hot rodders. Rebuild parts are easier to find than speed parts, generally, and can often be obtained from NOS parts suppliers.
Identification is fairly easy, with the biggest clue being its physical size - it is far and away the largest of the flathead V8 engines. The distributor is mounted on the rear of the engine, next to the fuel pump, versus front mount for the 239 and 255 versions.
Lincoln part numbers begin with the prefix 8EL (actually A8EL, but the A is usually dropped) and the Ford truck numbers with 8EQ. There are some important differences between the Lincoln and Ford 337s, but most internal engine parts interchange.