Possible, but VERY difficult!

Would require a donor card (of course)

And a heat gun to remove the GPU and RAM.

Also VERY L33T soldering and reworking skills.

In short, probably not worth the hassle!

It is impossible to solder BGA GPUs with regular heat-guns or hot-air stations. To un-solder them is very easy, but to solder a BGA chip like that one will need top professional tools and equipaments. Even RAM BGA modules are extremely difficult to work with... It is best to leave the GPU as it is, but to add a much better cooling solution and to replace only the memory chips with faster ones, maybe 5.5 or 5ns and the combo should then scale quite well up to 180+Mhz.
Just my oppinion...