I helped a friend replace his about 6 months ago. It's pretty
straight forward, remove the fan shroud, remove the belt, remove the
fan blade, etc.
If you have a service manual you will be ago, the new pump should run
you about 150 or so.
It the fan assembly is like the one in my 99 5.9L, you don't want to lay it
on it's side when you take it out, rather keep it in a verticle position -
something to do with the stuff in the thermal coupler.
http://www.pavementsucks.com has an article in their Tech section on the R&R
of a timing chain, which includes removing/reinstalling the water pump.
This is on a 5.2/5.9, but should be very similar to your 3.9.
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