Madmic,

Your 300Sd is not be dead, just wounded.

What happened is that the timing chain jumped, maybe because the chain quide failed, and the pistons hit the valves and one of the valves hit the cam and broke it.

Same happened to me in a '64 190D. All I had to replace was the cam, cam towers and timing chain.

Most likely the cam towers are broken too. I think they are designed to break to protect other parts of the engine like the valves, pistons, and camshaft. But sometimes it doesn't work and other parts are damaged.

You should be able to put the engine back in running condition by replacing the cam, cam towers, timing chain, chain guide and valve seals. Most difficult part of the job is to time the injection pump (IP). Put punch marks on the IP and housing and you should be close on the timing. If engine runs OK, as mine did, you won't even have to pull off the head. If it doesn't run OK, you might have to pull the head and replace some of the valves.

P E H