You won't want to use a coupe seat for anything other than a coupe. Other than that the only problem you should run into is matching the upholstry material as it changed over the production run.

__________________
1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)