I've read several times here from Stevebfl, Benzmac and others that the inline-6 timing chains really don't need to be replaced. They are very short and don't stretch very much.
Just my .02 cents.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".