In my opinion modding a GT500 has really become a waste of money. Lethal Performance has gone 9.70 @ 150 mph with a stock motor and manual transmission in a 2015 GT. So you can put a ton of money in buying parts or just get a stock 2015 GT.
https://www.youtube.com/watch?v=VPJJ2Q6CVRk
https://www.youtube.com/watch?v=VPJJ2Q6CVRk