99 crown victoria transmission question

I have a 99 crown vic that i bought at a police auction in feb of this year. My transmission recently went out on me, and I'm trying to buy a used one to replace it. I found one at a local junk yard, but they said they need to know if it's the right one. They said that it is a serial number on the trans that ends with either "ba" or "ca" and I don't know where to find it. If anyone knows it would be a great help.

It should be on the vertical (drivers) side...near the front (engine & bell housing )...;