'95 E320-water pump, radiator, head gasket

[tgmiller77]

The other day I had a nice pool of coolant under the car. The water pump is shot, I also think the radiator is leaking around the plastic seam. The car has 132,000 miles and is a 1995. The head gasket leaks oil like crazy and the gasket around the timing chain also leaks. My question is should I go ahead and replace the gasket while I have more room or should I just replace the bad parts and wait for the eventual failure of the head gasket. One good thing is the wiring harness has been replaced so I should not have to replace that in the process.
Where is the engine number on this car? I have found several numbers on the block, but which one os correct so I can buy the correct pump.

thanks