The 700R4 is a fantastic transmission!!! I put one in my S10 behind a very warmed over 350. It held up to everything that I threw at it. I liked the improved gas milage that the overdrive provided. It is my understanding the the L series transmissions are electrically controlled. If you are not putting the transmission in a car that is wired for it, the aftermarket box can cost up to five hundred dollars. Things might have changed since I looked into it but I would sure check it out before you leap.
Rick