420 SEL with snapped timing chain

I might have an opportunity to buy a 420 SEL (cheap) with a broken timing chain (which makes it not so cheap). Assuming it’s an interfering type of a set up for the valves. How extensive could be the damage? I have experience with some of the Japanese vehicle but none with Mercedes. Any ideas?

Thanks,

I would assume that most if not all the valves need to be replaced. Depending on the mileage and if you intend to keep the car figure in rebuilding both cylinder heads. Most likely the block is fine, and on 560's you will not need to worry(too much) about stripping the threads when you torque the heads back.