Page 2 of this thread explains exactly what is wrong with a large fuel pump on a stock rail. I would spring 100 for a new rail if i were doing this personally. Also it shouldn't make the engine run any more rich if the FPR is working properly.
http://www.mr2oc.com/showthread.php?...bro+stock+rail
Wolfkatz has some good info here too
http://www.wolfkatz.com/articles.php
you can buy a bored rail from ats for $75 or one from wolfkatz