I had a chain break on a 220D - my experiences were the same as those noted by Psfred. Two cam towers were broken, I reused the cam and did NOT even remove the head. I was able to snake the replacement chain back into place with a couple of coathangers but I did have to remove the IP pump and injection timer.

All this was done with the engine in place - not alot of fun but I think I had it all back together in one day.

Of course your mileage may vary...

Tim