Yeah, you would have to swap the heads as well. I just re-read your question and I got confused. Are you saying that the engine in the '79 300D has a leveling system and you want to use it's pump on the TD, which I presume has a bad hyd pump. I don't recall the sedan 300Ds having a leveling system.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section