Can I place a 722.6 from a '97 S320 into a
 

1996 S320? My trans is about to go and I have found a 722.6 for a good price.

No

In the E class at least, 96/97 were transition years where the trans went from 4spd to fully electronic 5 spd 722.6xx's.

Enter your vin below and note the trans data provided and shop for like kind.

http://www.mbclub.ru/mb/vin/?lng=eng

I'd talk to a friendly dealer before making a purchase.

I beleive the S320 got the 722.6 in 1997, but I may be mistaken. Getting all the computers to make it work would be fun.

Just rebuild what you have, it will be cheaper and faster.

You can't put an electronic transmission into a car that doesn't have the electronic infrastructure for it. It's the epitome of a hopeless project.