>this is the best way, if
>the engine still is
>in the car. Otherwise, there
>is no sure way to
>tell with any markings. The
>same casting numbers were used
>for 390 and 428s. 428s
>are very rare, and that
>alone would lead to a
>390 in the car. The
>428 cars were very special!!
>To tell the difference without
>any disassembly, you need to
>remove a spark plug. You
>then want to set a
>pencil or similar object on
>the piston and slowly rotate
>the engine. This will
>cause the piston and pencil
>to move up and down.
>The 428 have approx a
>4" stroke whereas the 390
>is closer to 3.75". No
>other markings will tell you
>for sure, trust me. I
>have a 428CJ Mustang and
>a 428 in my 69F100.
>I also have another 428CJ
>MUstang in my shop right
>now. They all have different
>markings, I have played this
>marking game for over 20
>years with FEs, its fun.
>