Will this fit or do I need to get a 3" flange????

Also am I fine with the stock heat shield or do I need to buy a new one or trim it???

 

You'll find that you will need to snip the heat shield to fit over the dp.. as far as the fitment the greddy flange is smaller than 3" it wouldnt be ideal. I say go with a cobb or pde dp, they both use donut flanges and would allow a better fit