The prevailing idea around here on the V8's is to replace the timing chain and rail guides at around 100,000-120,000 miles.
The chains on these V8's are very long (about 6' long if laid out flat), and stretch over time.
If your chain is hitting the cam cover, I'd replace it right away.
If you don't, it could skip a link and then you'd have valves crashing into pistons, etc.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".