My murray mower does not have a model number any where I have looked. How do I determine the model number?

Hi,
It has been on a tag beneath the seat for years and before that it was on the rear frame in back. It is generally a black on silver or white piece roughly 1 1/4" by 2 1/2". If you still do not find it, furnish the engine brand, HP and numbers off the shroud as well as the deck size. I can usually piece it together.
Peace,
Clarke