Sorry to hear of the loss. Good news is it is repairable.
Don't know where you're located, but in Sunny So. Cal. a similar 420SEL with low mileage of 135K and well kept, would fetch at least $4k more. You need to start shopping for a good independent MB Tech in your area, one you are comfortable with and can trust. A quality independent can do anything the dealership can do, cost less and they will tell you the little things, like change the timing chain AND rails around 100K.
Hopefully you only tried to start it once. Any further attempts to start the engine could cause more internal damage. You likely have a few bent valves, so you're looking at a valve job plus chain and rails now.
Wish I could be more help.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.