Also, to check the pressure I can easily install a gauge on the line but do I need to have the gauge readable while driving or can I just rev the engine up in park to get an accurate reading? If it's sitting in park and I rev the motor up will it show the max fuel pressure or do I need to be driving under a load?

You would end up with erratic fuel pressure using this method. The fuel pump delivers a constant flow of fuel, with the exception of the high/low flow voltages. However, the fuel used by the engine is constantly varying depending on engine load and RPM. The FPR maintains a ~43.5psi rail/manifold pressure differential regardless of load. If you measure the flowrate in the return line you would be suprised to see how much it varied.

Adding a restrictor post-regulator would increase fuel pressure when the engine is at low load and the return fuel flow is high, but at high load when the return flow is low, there would be significantly less of a pressure increase.

What you need is either an aftermarket fixed rate adjustable fuel pressure regulator so you can raise the base pressure to achieve a differential greater than 43.5psi, or an aftermarket rising rate regulator that will increase the pressure differential x psi for each psi of boost gained.

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If 8-8.8 psi at cruise yield 34 psi in rail and 13.0 psi [WOT] yields 43.4 psi.........this is a rising rate regulator with a 2:1 ratio so a 5 psi boost might raise rail pressure by 10 psi to 53.4 psi..................about a 10% mass flow increase.

Important to understand the real positive pressure being applied to the FPR so called vacuum port..........

If 8-8.8 psi at cruise yield 34 psi in rail and 13.0 psi [WOT] yields 43.4 psi.........this is a rising rate regulator with a 2:1 ratio so a 5 psi boost might raise rail pressure by 10 psi to 53.4 psi..................about a 10% mass flow increase.

Important to understand the real positive pressure being applied to the FPR so called vacuum port..........

A vacuum can only exist in space or lab............using the term on a vehicle leads to all sorts of confusions.

As far as including atmospheric into the calculations, I agree it's much more accurate but it is much simpler to use gauge readings for these basic things. Plus, if it is necessary to include atmospheric you must know what that is in your current location at the time you are taking the readings. In my opinion this is rarely necessary. For most it is understood that atmospheric is factored in. I'm sure you won't agree but that's ok

SuperHatch, your example make sense. The needle valve is just for restricting flow and since the flow will actually decrease during high load conditions the mod would be counter productive.