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5.0L (1979-1995) MustangTechnical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.
42, you shouldn't need any more or less pressure with the modifications that you have, the ECU will adjust around pretty much any small changes in fuel pressure. The only real way to tell is to get something to monitor your A/F ratio, and see what it is at WOT.
I'm no expert but i know i bumped the psi up a little bit after i got my car dynoed and it was running real lean like 16:1 a/f. I still need a new fuel pump though.