You can get 500 out of a stock shortblock, but not with what you got I dont think.
I think you are going to need a set of heads and a cam to make it to 500...And more fuel pump. You oughta upgrade the intank pump to a 255.

And injector size depends on how you fuel it. If you run an FMU, your injectors dont have to be as big. But FMU's suck. And if you dont know what ratio FMU you have, you are kinda in the dark.

To be on the safe side, the MSD BTM isnt a bad idea. It actually came with the Vortech kit. That said, the previous owner of my car used to have a pulley'd B trim on the car running 14psi of boost, low 400s on HP, and he did it without the BTM and no chip or anything. Just an FMU, 36lb injectors and a Pro M 77 meter.