Muncie M20 2.56 Wide Ratio 4 Speed Transmisson from 1964-1965! Date Code P0313 which is March 13. Number for the main casting: 3851325. Other Part Numbers: 3857584. There is a chunk missing out of it that will not affect its function, but please view pictures and note the damage. Shifts through all gears smoothly, works very well! We cleaned up the outside and she looks beautiful!