Use mild steel, I have built a few turbo manifold/headers for a couple of non MB cars. I used mild steel ells and primaries with milled barstock plate for the mountings. Very nice and easy to work with. Just make sure you get quality stock.

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MB roster
'85 500SE euro Ratrod
'92 500E's x2 / '94 E500 stored
'91 560SEC w/43K stored
'92 Cabby 16V OE 2.1 AutoX car
JDM RHD cars now.