I've done a timing chain on an M119 engine and I don't remember it being any more difficult than any other chain I've replaced. My upper chain guides are as brittle as glass and you have to be careful that you don't drop any guide pieces into the engine.

I did have to buy a different crimp tool - the jaws on the tool used to crimp the chains on the OM60x, OM61X and M103 engines were too large to properly crimp the pins on the chain used in the M119 engine. The only other tool I bought was a set of pins that are used to lock the camshafts in position at a specified position to check the valve timing.

I did the job by myself and it certianly did not take 6-10 hours, YMMV.

It certainly would be better to remove the front timing chain cover and renew all the chain guides but it's quite a bit more work than just rolling a new chain in.