so... what exactly is the stock fuel pressure?

well it depends on wether its at idle or at 0 psi or at full boost. Here are the #'s

Idle = 26 psi
Zero Boost = 36 psi
Full boost (assume around 12 psi) = 48 psi

*for every psi of boost you add 1 psi of fuel pressure.

Thank you. My friend wants to know what to set his fuel pressure regulator at with a Walbro high pressure 255lph pump

well the FPR is mostly for idle and low boost so i would say you want to set it to 26 psi