A lot of vehicles that people consider doing the LS swap in already come with a healthy 700R4. If you want to save money by keeping your current transmission, it can be done. The most difficult issue that you will run into would be where to mount the TV cable. The transmission itself will bolt to the LS series of engines.
You need to just take a few things:
A Crankshaft Spacer: This lets the torque converters from the Gen I transmissions engage the crank on the LS engines
Somewhere to put the Kick Down/TV Cable: You will need to purchase or build a custom bracket to hook it into.
ECU Retune: The engine has to function on it’s own, without thinking it’s speaking with the transmission, or things could go wrong.