I have a '76 300d and have gotten many salvaged parts off 240's. The 115 body is the key for body parts. As I undrestand it you car is the same as mine except for engine, tranny, luxury featurs etc..
Think of it as an DX, LX , LXi hiererachy.
The W114 /115 body was produced from '68-'76. Ther are subtle differences between 114 and 115. I have even found some interior parts from early 123's to be the same as mine. E-mail me if you have vacuum probs as I have just completely gone through mine.