I have a Metallic-Blue, 1980 M 300D. The engine's compression was low in 2 cylinders, and would now start, so I replaced the engine with a 1979 issue 300D M. engine. The 79 engine has different spark plugs(big) & relay harness & relay, also vacuum module on top of the fuel injector. I have both harnesses, and relay boxes, and injectors. How should I resolve these problems, especially, the glowplug-harness, relay problems. Thanks in Advance. Sure could use some help with this! James