Can I run my 96 impala trans behind my gen 3 5.3? If so what has to be done?

 

You could, but you'd be MUCH better off getting an LS 4L60e.

To run your existing transmission, you'd need a spacer for the crank, and some of the bolt holes won't match up.
4L60E cores for these engines aren't that much, just get one out of a truck and have it rebuilt (or do it yourself; there are some really sharp guys in the auto transmission board).
You won't be sorry.

 

Answer...Yes. I am in my 94 that's getting an LS2. Reason being it's a $3500 trans and $900 converter. But no different than a th350 usage. Get the SFI dual pattern flexplate and center adapter from Speedway.
A 0411 PCM will run the trans. A good tuner will know what to do with the TCC lockup controls in the tune.

My car was previously LTx , 24x swapped, so the PCM was tuned for it. But now it's getting the Holley termi max kit.