Engine year?

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2002 300m i had to pull engine to install new crankshaft and i noticed this isnt the original engine. It does have aluminum block and its a 3.5 but my plate that holds the rear main seal is a oring and my oil pump is oring gskets ..everything i look at has paper gasket in rear and a metal plate attached to rubber for the oil pump. How can i find out what my engine is. ...engine cast#is 4663806AB