Completed the bilge blower installation and I'm VERY happy with it. My main objective was to remove gasoline fumes from the bilge area before I do any work in the aft bilge (it gives me a headache to work in there right now), and to be able to move a little bit of air through the entire length of the bilge to air it out occasionally. Some points:
1. The West Marine 3" blower is a re-branded Atwood as far as I can tell, for $30, $12 less than the Atwood. These blowers will reportedly only last for ~ 300 hours, but that's a lot of run time for something I plan to use infrequently. The airflow and noise levels are both very satisfactory.
2. With the 3" duct elbow pointed 45 degrees up to port side, and protected by a vent hood, even if a wave crashes into the engine well, very little water should run into the ducting, and if it does, it will run right past the motor and simply enter the bilge. No big deal, and this would be a very rare occurrence.
3. It draws 2.3 amps, 0.6A less than advertised. That said my ducting run is stupid short - just enough to get the blower to about the top of the stringer level.
4. I was VERY happy to note a small, but certain, amount of air being sucked into the forward bilge compartment in the cabin with the blower on, so indeed, even with only 1" limber holes through the various bulkheads of the bilge, a small bit of air is moving. I still would recommend future builders use larger limber holes in the bilge to let more air through - there's no reason not to.
Looking through my remaining to-do list, this is the last electrical installation, so now I can finally secure the main wiring bundle and install protection over it in a few places. THAT makes me very happy