In that case Colin your fuel pressure reading won’t relate in any way to the fuel pressure (indicated as fuel flow) on the old gauge.
I guess that indication will be useful for diagnosis of a failed fuel pump (either of them) once you get used to the normal indications in cruise.
Where will the pressure be sensed? If it is in the pipe from the fuel servo to the fuel distributor, then you need to watch out on how that is done because that is exactly where the transducer for a fuel totaliser goes (on a correctly done installation, not the Socata/DGAC-bodged ones which could not be corrected legally on an EASA-reg) and you need to avoid turbulence in that pipe.
