Unfortunately it seems maybe your fuel gauge doesn't seem very accurate because it starts off at 10 or 11 psi then jumps to only 40psi then settles at 32 psi which may or may not indicate you are missing out on a 10ish psi reading.
Does/did the gauge start off at 0 psi for any of the earlier/first tests?
Your actual over all psi should be 43....If your gauge is off 10 psi then you might only be getting 33 psi and resting at 23 psi. which if so/yes, that's to low to start the engine.
Where you ever able to start the engine with help from the fuel spray test you did?
Here's a video of someone else testing their Mercruiser for reference points,
He removes the vacuum hose line at one point from the fuel regulator which helps gain 3 - 5 psi while engine is running...That's normal "usually" telling you the regulator is working okay.
One trick you could consider trying would be to get separate fuel tank and a "outboard fuel primer bulb" and create some of your own fuel pressure by hand to see if it help start the engine any, 'Possibly clearing away some debris should there be any and to maybe help clear the debris out first, remove the upper fuel regulator up on the fuel rail and catch the fuel flow to try and not make to much of a mess of things...Turn your batteries off first though should you try this.
Also you'll want to know that the regulator up on the fuel rail isn't used as a fuel regulator to control fuel psi, it used to dampen/lower the fuel pulses for the fuel injectors.
When did you install the 1 on the rail? Before or after the engine won't start?
Plus where did you buy it?