I had a GF3 Ti 200 made by Laedtec (winfast)
I also had to replace the fan assembly, it is fairly straight forward.
They are mounted by 2 or 3 plastic retainer clips.
Unclip one and replace it with the other BE SURE TO USE THERMAL PASTE between GPU and fan assembly.
If you have done a CUP sink and fan you will find this easy.
Make sure that the new sink and fan is compatable with a GF 3