I am in the process having two 540's built. My engine builder and I were talking today and he suggested maybe using a Quick Fuel Technology Professional Series carburetor, instead of the 1050 Holley marine carb that we were supposed to use.
Any thoughts on that?
I told him I would like to stick with the holley Marine carbs, are there any advantages or disadvantages?

Let the coast guard find a non marine carb,,, or have an incident and have your ins company find a non marine carb and there will be issues,,,just not worth it to me.

Theres a good reason for marine carbs and the cost difference isnt worht dealing with, ecspecially gettin tied up if u get sued and ur insurance wont cover it.................

I would not recommend using anything other than a marine carb. Call Dean or Brad @ Nickerson performance. They will set you up right the first time with the right carb.

As a marine surveyor I would highly recommend not using a non-marine carb. The overflow tubes on the top of the marine carb are bent 180 degrees to return fuel to the carb instead of blowing it straight up like a automotive application does. There could also be a issue if the carb has a electric choke that does not meet marine standards for ignition protection. My two cents.

Here here to all of the above. Hope you take the advice and don't risk lives over it.

So can 4150s or dominators be converted to marine carbs or is this not feasible?

I had the J-tubes installed on my 1050 blower carb. Had the standard shafts though. At what point will it be considered a CG approved carb?

Aren't the shafts sealed to the main body on marine carbs? I would think they would have to be to prevent fuel from leaking out if the carb was to flood through the "J" vent tubes.

I have bought J tubes for some other guys, but as you said, that is not everything that makes it a marine carb.