First off.....
http://www.peachparts.com/shopforum/showthread.php?t=217243&highlight=rod+bender
Therefore look for a 300SDL.
The 560SEL was the only model in the range to have most features as standard (Heated seats, powered rear bench) The diesels usually lacked those so if you do find one with them it's good. The 350s have the updated interior and did usually have the passenger side airbag which in the 300SDL was usually a glove box. The 560SEL has a somewhat different rear suspension setup then a 350 which lacks the hydraulics.