[undy]

Don't go to a dead head single line system. What you have now, as far as good fuel pressure regulating, is far superior to a single line system. Fix what ya got!

I run a Holley black, which is externally regulated, and I have a "Jegs" billet return style regulator. The fuel pressure stays dead on 6 psi all the time. The Holley Black should be good for around 650 to 700 HP too. It feeds my KC 482 quite well.

Just a side note.. I'd hang a volt meter across the electric pump while it's running. A fluctuating voltage source could cause these issues too.