will stock injectors flow enough? And if turned up will the stock pump supply enough?

it really depends on which injectors. Most are pretty big already.
It will be really lucky to hit 280hp with everything maxed out.

Wow that little? That turbo supports 650-750 on the 6.7 cummins. I guess it's pushing a ton more fuel..

Exactly. These engines are really held back by limited fuel. Drop in a 13mm Ppump, and it will really start breaking stuff.....maybe laying some patches of rubber.