I would look in your local Craigslist for possible engines/trans. Be sure to get the harness and computer with it to simplify the installation. If you do get the original harness and PCM, the PCM will need to be "flashed". Basically a term meaning it will need a reprogram removing the VATS(Vehicle Anti Theft System). All other emissions programs should remain intact for your emissions friendly install.

If you decide to run the 4L80E, you will need to shorten your driveshaft as well as get the driveshaft from the donor vehicle to get the yoke for it.