With enough $, you can put any engine in the W201. That said, if your wallet doesn't need weight loss, then you're best off sticking with another 2.3 engine since to drop in a 2.6L you'll need to replace the cooling system and the front mounts, as well as updating the front suspension and brakes for the extra weight. Unless you have a readily available donor car, it might be more cost effective to just buy a whole 2.6L
The US '85 was the first revision of the M102 (thanks sixto!) engine from the '84. The fuel injection system went through a subsequent change sometime in late '86 or '87, (added the R/16 resistor) so to upgrade to those engines, you probably have to change out the ECU and some other relays.
Last edited by MTI; 06-07-2003 at 11:57 PM.