You can't rely on casting numbers -- the only way to tell a 390 from a 428 is to take off a piece of the engine and peek inside. Actually, you can't tell a side oiler from a 390 in our cars because you can't see under the car to find the cross-bolts without jacking it up (much less to see the side galley) and it's too hard to use a mirror. A 390 with the extra webbing that can be bored out nicely and is stroked to 445 is just as good as my 428CJ that is bored out to 447 cubes. I have a shorter stroke for faster revs (and a slower piston speed), but that's mostly bogus.
