The biggest problem with figuring out injector size is what BSFC to use. The modern day heads, cams, and intakes (mostly head chamber design) are getting todays engines in the .36 to .42 BSFC range.
You can also run the injectors up to 85% to 90% duty cycle (DC). I prefer to size them at 85% DC.
The other side of the coin is at what RPM is the HP peak going to be at. The higher the RPM the larger the required injector. This is due to the time available to inject the fuel getting less and less. For a DC less then static there is a finite amount of time to open the injector. This eats into the actual time the injector is flowing fuel.
With all that said, at 475 HP, negating RPM limitations, at 85% DC, and .40 BSFC:
475 (HP) * .40 (BSFC) = 190
190 / 8 (injectors) = 23.75#/hr
23.75 / .85 (DC) = 28 #/hr
If willing to go to 90% DC:
23.75 / .90 (DC) = 26 #/hr
Running them static with 24 #/hr is enough fuel too. Can also run the numbers with a BSFC of .36. Don't need much injector at all then. Of course using a BSFC of .45 would be a more conservative approach.
And, this is for an N/A engine, boosted apps use BSFC in he .55 to .60 range.