A 255 pump will cause a restriction because it's trying to flow 255lph through a tiny feed line. The restriction will be caused on the return side and not allow the fuel pressure regulator to function properly. This will show up on a gauge as a higher than normal fuel pressure with a unsteady needle.OP: The mods suggested by the tuner look fine, all except for the fuel pump. For 400 RWHP, a 255LPH pump will be sufficient. (Calculations show that a 190 is actually adequate, but the 255 gives a little head room.) A larger pump does nothing but recirculate the unused fuel, raising its temperature. You can see my mods in the link in my signature if you're interested.
EDIT: And would a full AN fuel system be nice? Yes. Is it needed for your goals? No.