It is actually a pretty simple procedure, we do it on old Jaguars all the time. Next time your 600 needs a pump I would seriously look for someone who will rebuild it. The last one we did the new pump would have been near $2000. The rebuild kit was less than $200.
The 600 has an engine oil fed viscus coupling similar to a small torque convertor on the front (I presume thats why its so expensive.)