You use the wide band as a check. You can use the fpr to set the pressure, and run the wideband kit to check the actual air fuel ratio. The stock sensor creates a constant wave form when its operating properly. They are hard to read for tuning purposes. You use the wide and to check your air fuel ratio under power, it should be somewhere close to 12.5:1 wide open hard running. If it runs leaner (above 12.5:1) you would add some fuel pressure to get a bit more fuel and make the proper power it's capable of. If its rich((less than 12:1) you would take some pressure out. You do not want to drop the pressure much, anything less than 35psi would cause insufficient fuel atomization. You leave your stock oxygen sensor in because it will automatically adjust for proper cruising air fuel ratios on its own. Once you get to heavy loads, the computer ignores the oxygen sensor and runs off the base map, which will cause lean or rich problems with improper flow rates.
1991 Mustang LX 2.3L 5 Speed convert
1989 Ranger 4X4 2.5L 5 Speed solid Dana 30 front axle, 4.5" suspension lift, 3" body. ( blown up....)
Entire turbo kit waiting to be used again.