I need to change the water pump on my father in law's "old" truck. Its leaking very badly, not from the front, but the back of the pump :scratches head: something I've never seen before. But anyway how bad is this to change?

Not hard at all. Search the forum for water pump & you'll find
details & tips. GOOD LUCK

Not that hard at all. But, I ran into trouble trying to unscrew the Fan Clutch from the pump, broke two $90 tools, and ended up cutting it off to save the pully and had to replace the clutch too. It apparently "cold fused" together.

The special wrench for the fan blade is huge waste of money,too thin.Here is another way,use an air hammer with a really long chiseling bit.Put the bit towards the end of the flat of the nut with pressure on it.It should come off.That is the way I do it.Keep the belt on when doing this