Set it at 39 with the Vac hose disconnected....Myself I would run a few days and check the plugs...If they look good...Leave it alone...39 is about what your stock FPR is gonna run anyway...
39psi with the vacuum hose is off. Might wanna verify that it drops to 31 or so when you hook it back up, and also that it jumps to 39 when you open the throttle.