Well depending on where you live, you may or may not have to deal with smog issues and registration. Also this kit doesnt address the weaker trans and you will not have all the other features a gtp has (performance shift, hud, ect ect) plus you will still have to modify ecm, and Im sure you will run into some other problems also. With the stock GT engine running at a higher compression ratio, you may also damage the pistons/engine easier when you try to boost more pressure. Ive seen people crack there pistons on a GTP (which I believe are stronger than the stock GT's) so thats something else to think about.
But it is another option for you. Good luck with whatever you decide.