on your current MB's you can do it on the mid-90's ones. I would advise going ahead and spending the $ to get her a '94-95 E320. Make sure you get the records with it and that the cyl. head gasket has been changed along with the wiring harness. You will like it alot better than the C280 series. I get around 26-27 mpg with mine when I drive it.
Jim
'85 300D turbo
'95 E320
'97 Honda CRV (wifes)