fuel pressure for nitrous...

With the "Holley" style regulators, you have to set them with fuel flowing. With the fuel not flowing, the regulators tend to get pressure creap.
PS: with the numbers you gave, I think you will be too lean.
With a fuel pressure of 6 PSI, nitrous bottle pressure of 950 PSI, nitrous jet of .047, you should use a fuel jet about .043. That will give you just about 100 hp engine.