You can't just pull the stock FPR and run the pump. You can get a return style setup and then disregard the stock FPR and use a aftermarket FPR. Then you'll have to buy a fuel rail, lines, fittings and modify your fuel cage to make it all work.
There's a small number of people here running an external FPR, and the ones that have that, is because they ran a return line.
You're doing a Greddy Kit, there's plenty of information about it and the mods to achieve more power. Like I told you via PM, just get the Walbro 255lph and that's it, no need to run an external FPR unless you want to spend $500-$600 on a return system