Once again, please remember that I am no mechanic.
Anti-siphoning valve: If you’re going to install them, there should be one per fuel line. As per you picture, you would need three. Install them as close to the tank as possible. This will keep the maximum amount of fuel in the lines at all times. Yes, I have heard of them jamming up occasionally. I view this as a minor problem. I would rather replace a $2 piece and solve the problem, than tearing apart an entire fuel system trying to figure out why I can get gas to the carburetor.
Fuel pump mounting: My fuel pumps are mounted on top of the motor. It looks like we may be using the same kind. Mounting them on top of the motor helps them work better. Most people forget that although the pump is pulling fuel though it, it is also pushing fuel out of it. Pumps are designed to pull fuel. If the distance from your fuel source to the pump is less than the distance from your fuel pump to the carburetor, your pump is pushing. Most pumps do a good job of both pulling and pushing fuel through the line. Unfortunately, in this situation, our older boats were equipped with mechanical pumps that were stronger and could handle pulling fuel from the tank and pushing it the full length of the boat if necessary.
The Smell: On my boat 1978 Catalina 350, there are hollowed out areas underneath each engine that are designed to keep anything from falling/leaking from the motors, (Oil, fuel, broken spark plugs), from getting into the central bilge. From time to time this area gets something in it. Like any part of the bilge, it should be kept clean. Not sterile, just clean. Use some simple green or any non-corrosive degreaser. I have heard that foaming carpet cleaner works well. Spray it on, let it set for a few minutes and wipe it of. If you’re worried about any chemicals eating your hull, Rinse the area with clean water.
Carborators: Edelbrock 4 barrel 600cfi marine carborators are expensive. If you buy them retail from a marina or dry dock, the are about $490 off the shelf. Search the internet, You can probibly find them for half of that. This was a hard lesson to learn.
If your curious about mounting the fuel filter on top of the engine, let me know and I will get some pictures for you.
If you have any more questions, don’t hesitate to ask.