Here is a pic of my then traded-in 99 ML320 (W163) next to the newly purchased 07 ML350 (W164).
You can see by the pics that the W164 grill insert would not be compatible with a W163 hood.
Not sure what look you're going for, but there are later W163 grill styles available for your model here and on eBay:
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btw, I opted for the chrome grill strips on my W163...procured from eBay.