How long will a M127 engine go before needs rebuilt?

[Marrs]

What is the typical mileage I can expect from my '62 220se engine before it needs to be rebuilt? I realize many factors exist that can change the useful life but let's assume it's a typical engine with better than typical maintenance (tho probably typical for users of the forum). I'm specifically talking about the engine life from wear not things like failed head gaskets, etc. and specifically this engine, not Mercedes in general.

Also should the timing chain be replaced at 100,000 miles or really only when it shows signs of noise, wear, etc?