Here's what i know about 34xx CATs
A 3406, 3408, 3412, 3416 all use the same rods, pistons, cylinders, heads, gaskets, rings, bearings, etc. 2 cylinders per head. The last two numbers denote cylinders.
All parts, other than manifolds, block and crank are interchangeable in the 34xx series.
The rest, who knows?

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport