Hi Simon, I just did the pump on my 300TE, and with some advice from the good people on here it was quite an easy job, I took my time and used the new seals that was provided with the pump and all went well.
Good luck and let us know how it goes.
It is probably the straight six twin cam engine and book time is of the order of 6 hours.
I bought a genuine Merc pump because I did not want to be doing that job again in a hurry, and as the car is a keeper it should last another 150K miles.
Hoses and pipe seals and thermostat and fresh coolant (again Merc because it is ph neutral and will not be eating your internals and causing sludge build up in the passages) Also water from Halfords not the hard tap water.
The big secret is to have thin quarter inch socket and wobble set to access the in-accessible inner two pump bolts.
So a fair amount of front engine dismantling and with the front engine coolant pipe and the one going to the rear engine heat exchanger make sure you renew all pipe seals.
See russian diagrams.
When draining coolant a reminder there is a tap to empty the block, on right hand side of block.