maybe it is possible, maybe it is not. Some how I doubt the supporting components on the board are exactly the same.
But where do you think you'll find this GPU?
If you have some serious BGA tools maybe you could pull it off but you'll need a lot more than a hot air gun to do it. You're gonna need a proper hot air station, hot plate/reflow oven, reball setup, and some serious BGA skills to get it done.
I think you're time and money is better spent on a new/used PS3 slim and PS2 and just sell off the old one before it dies.
If you seriously want to try it for fun then research the leaked schematics and see if the boards are compatible. But I seriously doubt this is a viable project.
The worst part about people saying 'Just Search' is that if you are not familiar with the site you don't know what terms search for. On the flip side if you do read the site daily all you see is the same 20 questions over and over and it is tuff not to be a douche.
Slim 160GB CECH-2501A