You're looking for an M103 engine, and considering the sedan, coupe, and wagon, right?
Well, it's more complicated.
1990-1992 300CE's got an early version of the DOHC M104 engine. It didn't have variable valve timing. It has the same HP as 1993 and later M104's, but at a higher rpm (217 hp @ 6,400 rpm, as oppossed to 217 hp @ 5,500 rpm). This engine also developed less torque ( 195 lb/ft @ 4,600 rpm as oppossed to 229 lb/ft @ 3,700 rpm). Variable valve timing really made the power curve longer and flatter.
So, if you want the M103 engine in the 300 CE's, you're going to have to look at 1989 and older models. The problem is that MB sold relatively few coupes - about 2,500 / year, so they may be hard to find.
I also got all this info from the following page on MB USA's website. It's impossible to navigate to this page from the home page, so if I were you, I'd bookmark it:
http://www.mbusa.com/brand/container.jsp?/overview/overview_engine.jsp&yearModelCode=88_E300S&class=88_E&rnav=024568&menu=2_2
1990 - 1992 300 TE's all used the M103 engine, but I think there'll be few to look at - they only sold 1,174 wagons in 1990, 1,196 in 1991, and 1,492 in 1992 in the U.S.
So, your best bet will probably be the 1990 - 1992 300E's. They sold from 9,600 to about 12,000 cars / year so you should have no trouble finding nice examples. Coupes and wagons will be few and far between.