how do I dentify the model transmission in my 96 SE

Being a 96, you'll have the 4T60 model of transmission.

Then the only question would be, what gear ratio is in it?

Easiest way is to look at the sticker on your spare tire cover in the trunk.
I usually look up the possible gear ratios on Rockauto by looking at axles. Those including the three character code for the gear ratio, which then tells you which trans gear ratio.