Hi leighton,
Actually it's not a stupid question. Your reasoning makes sense, since their both Mercedes engines and they both have equal displacement, the diesel turbo should work on the gas engine. In fact it would work,, however, not very well. You see, a diesel engine does not move as much air as a gasoline engine due to it's lower RPM range and high compression ratio. Since a gasoline engine of the same displacement flows more air, the diesel turbo would only be good for the bottom end of the rpm range. The turbo I pieced together is completely matched to the M103's rpm range and air flow. This will give me "the best bang for my buck" through a large portion of the M103's RPM range. As is the diesel's turbo is matched and will give great boost and flow for it's corresponding RPM range. You can see where I was at the beginning of this thread. I have learned A LOT about turbocharging since then. I would highly suggest getting a book on turbocharging if you plan to turbo your 300CE. These M103/104's (I don't know what you have in yours) seem to be great candidates for turboing due to their extremely well engineered parts. Every master engine builder I show the parts of this engine to are thoroughly impressed with the design and engineering. From what I see, so am I. Feel free to email me if you have any questions on your project, I will be glad to help. Also I plan on offering a kit when my engine is done. You may want to wait for that if your interested in getting up to the 400hp range. I'm not looking to make much money on the kit and it will save you from all the crazy math and hours involved. Let me know if your interested.
Good Luck!
Adam