OSO People,
I finally got my 496 fired up for the first time since in my possession (out of the boat). Overall, very happy... Couldn't find any leaks, manifolds stayed nice and cool, good water flow, etc...
I monitored everything on my diacom and analog gauges and all was within reason.

The one thing thats bugging me is the fuel pressure. When I turn the key to the on position, the fuel pressure will rise to about 45-48psi and settle down to about 43.. Once I start the motor and let it run at idle, the fuel pressure drops down to like 34-35psi and hangs out around there.. From everything I can find, the pressure should be in the low 40s, but I also saw something floating around in my search results that the pressure should be checked with the vacuum line disconnected from the regulator, but that doesn't sound right to me.
Just to recap, This is with a revised cool fuel 3 module so no peeling paint.. I've also had it completely apart and replaced all the filters and had the injectors cleaned and flow tested. I'm also using a short piece of 3/8" fuel line on the suction side to a jerry can so shouldn't be any inlet restrictions.

Anyone have any insight on this? Thanks

Removing the vacuum line shows the max output pressure of the pump. At low-load conditions, where there's increased manifold vacuum, the regulator will reduce the delivered fuel pressure due to vacuum on the diaphragm in the regulator. Removing the vacuum line allows you to see exactly what the regulator and pump are providing.

So with the engine out of the boat, I don't really have a way to put much of a load on the engine, so do I just try removing the vacuum line while running to see if the pressure goes up to at least verify the fuel pump is supplying more pressure and the regulator is doing its job?

Right. The removal of vacuum duplicates some aspects of the high-load condition to show you what would happen to the pressure.

A weak pump, of course, might deliver enough pressure at the volumes needed at idle, but could fall short at higher rpm fuel demands.

On my 496HO with a whipple supercharger, the fuel pressure will be about 43 at idle with the vacuum line NOT connected. When you plug it back in it drops to around 38 or so. Just like what Drfeelgood is saying.

So just to double check myself, I ran the engine again and paid extra attention to the fuel pressure. It was closer to like 35 at idle, but when I removed the vacuum line, it jumped up to 43ish.. So I'm going to still assume thats within normal range.. I'll get a better feel for it once its in the water and I can do more testing under load but for now I'm gonna assume its good.