Wow, been i while since i did all this but no, water pump is separate to the timing on the GT..
There is an aux belt that goes round the crank pulley, then the adjustable tensioner (at bottom, its like a idler on a triangle plate, hard to describe but undo the triangle plate a bit and you can slide it to adjust belt tension), then to the alternator, from there it goes up around the waterpump pulley and back down to crank.
Then behind that aux belt there is another that goes from waterpump upto the pas pump, no idlers or tensioner, you have to move the actual pas pump with an adjustment screw to slacken the belt and then retighten wihen you replace it.
If your car has aircon then there is gonna be another belt, it will have to come off first, its the front belt on the crank pulley and goes forward to ac compressor, removed by slackening adjustable idler on top of belt.
Just getting to here and having the belts off will result in much swearing lol.. But now, if my memory serves to actually get the pump out you need to put a jack with bit of wood under the engine and loosen off the engine mount on the belt side so the engine can drop down enough for you to be able to get the pump out past the cars body.
Then there is what do you replace, as replacements come either as the pump with housing, or just he actual pump part.
so.. like this, just the pump and bit easier to change
Or like this, complete with housing. I'd try go for this unless you a 100% sure there is no leaks between the housing and engine etc. Can always split the new pump part off it and just use that if you want to as well.
All in all, not hard but fiddly and will take alot longer than you first think... But thats seems pretty standard when you try do anything on the GT i found when i owned one lol.