The stock fox fuel pump can barely supply the stock motor much less any upgrades. Its what like 88lph IIRC? Drop the tank, do a 255 walbro and call it a day. Upgrading your injectors to 24s couldn't hurt but the 19s should be ok for what you have. The bigger issue is the injector condition after all these years if they are originals. They stop so much spraying a fine mist of fuel into the cylinders and just squirt a jet of fuel in instead. When I did the injectors on my Cobra from OEM injectors circa 1995 to new ones it cured the rich idle condition I was having and the car picked up a noticeable SOTP gain.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.