The main differences are emmissions.

The 78-80 300SD engine had the non egr manifolds. They tend to never carbon up, which is desirable. If you take a newer engine, i would probably take the other stuff off the existing engine, if its still there.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes