So let's figure 600 flywheel hp, instead of 550, just to be safe.
Using a BSFC of .85, we have 600hp x .85 BSFC = 510 lbs/hr fuel flow total required.
For what injector we need, we take that 510lbs/hr and divide by 6, so we have 510lbs / 6injectors = 85lb/hr injector requirements AT 100% DUTY CYCLE. To be safe on your injector duty cycle, you would want 100lb/hr injectors
minimum.
For fuel pump flow, we know that our total fuel consumption is 510lbs/hr to make 600fwhp. Using a base pressure of 45psi, and figuring 30psi of boost (on the high side to be safe), we get 75psi for the fuel pressure that needs to have 510lb/hr, and just to be extra safe, I add another 5psi to make it an even 80psi fuel pressure that we need to make sure our fuel pump(s) flow 510lbs/hr for us.
510lb/hr into gallons per hour (gph) is done by 510lbs / 6 =85gph, so we need 85gph at 80psi...
The Racetronix site says that the 510lph dual 255lph pump setup, at 80psi and 13.5volts, flows 345lph.
Using a simple online conversion calculator, we get 345lph = 91.1 GPH...
So, if you need 85gph to make 600fwhp, and the 510lph setup flows 91gph, you could probably get away with it if you don't intend to push it past that power level.
If you ever think you are going to want more than 600fwhp, I would get a dual 340lph setup, or go with a big external pump
Hopefully that helps!