Injector size?

Is it true what I was told.....that to find out what the minimum size for your needed injector is take 1/2 of your HP and divide it by the # of cylinders? Is there benefit to having a larger injector or fuel pump than needed, or will it have an adverse effect???

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'90 LX 5.0; 12K original miles (no sh*&); 3.55 gears; pulleys; Edelbrock Performer Heads;
BBK shorties; MSD 6AL ignition system; Motorsport E303 cam; 75 MAF; 70 TB; Eibach spring kit;
Southside sub-connectors; K&N cone filter charger; Hurst shifter; fiberglass cowl hood; A/C-less;
rear seat-less; cat-less; Flomasters; Corbeau racing seats (fronts); 12.513 @ 108 mph