I have a metallic blue 1980 300D, Merc. the engines compression was low in two cylinders, so I replaced the engine with a 1979 issue 300D M. engine. The 79 engine has different spark plugs (filament type, and relay harness, and relay, and vacuum module on the top of the injector). I have both harnesses, and relay boxes, and injectors. How should I resolve the glow-plug-harness, relay problem especially. Thanks in Advance. Sure could use some help with this! James