Engine numbers, for engines up to 1974.
To find the engine number for slant six engines, check the passenger side of the block just below the head. For V8 engines, check the drivers side front of the block below the head.
The engine number contains the build year and engine displacement. It may contain an assembly date. The assembly date may be as simple as 3-15 (March 15th), or based on the 10,000 day calendar (2787 = March 15 1969).
The simple date is decoded like the so number on fender tags.
The letter before the number is the model year A=1965,B=1966,C=1967,D=1968,E=1969,F=1970,G=1971,H=1972,J=1973,4=1974.
You can also tell the block displacement by the casting number. Often,
but not always, a casting date may appear on the side of the block.