Cutlass Supreme SX - is it genuine

I have a 1970 Cutlass Supreme SX (at least I think I do). I was the second owner, acquiring the car when it was about 9 years old. I came across a website - www.sx455.com -- which has spotter tips. All the tips match up, except I am not sure of the engine in the car. I know it's two barrel. It has the numbers 396021 stamped on it (I do NOT see the F or F1 following the numbers though, which www.sx455 say should). There is also, however, a paper decal just before the radiator. The paper decal talks about it being 350 C.I.D. (and not 455).

Can anyone help me with my confusion and how to tell for sure what engine is in the car?

Thanks.

[jethro442]

396021 is defonetly a 455 there should be a F (68-72) or Fa (72-75)on the right side of these numbers as you face the motor from the front .The F,F1,F2.... is on the back of the block behind the fly wheel that is the casting run number. On the right front side of the motor under the head where it meets the block there is a small pad with nubers on it. These should match the last six numbers on the vin if its the origenal motor.

[ January 03, 2005: Message edited by: jethro442 ]</p>