I'd be curious to hear how this goes, as this is something I've often wondered about.
Long ago, I purchases an adjustable fuel pressure regulator from evoluzione.net (I think they actually sold some Guzzi bits at that time). Anyway, they indicated that the fuel system on the Guzzi was the same on some Aprilias, and those were known to deviate wildly from spec, hence their aftermarket solution.
I never got around to installing it prior to my bike going in for the "never-ending rebuild" project. Now that the bike is back, its running so nice that I'm reluctant to mess with anything. Even if the stock regulator on my bike is correct, I'm still tempted to put the adjustable one on, just so I *know* it's correct. Or, I guess I could probably figure out how to fit the gauge from the kit with the stock regulator just to see what it's doing.
__Jason