I do not have experience with the Holley 1900 carburetors, but a friend of mine used a street Demon on his Challenger 383 engine and is pleased with it. I was thinking if I went with Holley, in my case, I would like to replicate most of the appearance of the original Holley 4160s on the standard 440s in 1970 on my Chrysler 300s and also have the external bowl vent that they had from the factory to keep fuel temperatures at a minimum compared to internal bowl vents only that all carburetors have. Those external bowl vents in 1970 were plumbed to the breather cap so that fuel vapors would go to the crankcase, but I would not do that for various reasons such as oil dilution, etc. So the modern Holley replacement that I was considering was this one, or one close to it, although it is pricey:
Holley 0-80451 600 CFM Stock Replacement Carburetor - Holley Performance Products
I might add that carbon canisters are for the purpose of capturing evaporative fuel vapors from the fuel tank and from the carburetor bowl to prevent HC emission from escaping into the atmosphere and creating smog (HC + NOx emissions react in sunlight to create smog). Carburetors with external bowl vents also have a purge port to purge or clean the vapors out of the carbon canister to keep them available to store more vapor later (the primary purpose of carbon canisters is not really to keep atmospheric pressue in the tank, although it does serve that function too. It is to store excess fuel vapors). I like the external bowl vents for keeping fuel vapors from going into the engine on hot days and creating hot start problems and for keeping the fuel cooler than it would be without one, thereby minimizing the potential for vapor lock. I have never experiencef fuel spill over on any cars that I have ever had with them.
I would personally keep EGR on your engine, but use one of the smaller diameter valve openings. In this way, using today's crappy low octane gasoline, you can advance timing a little more than without EGR and get better overall fuel economy that without EGR. Most modern engines have EGR for maximizing fuel economy and keeping higher compression ratios and even the turbo engines use it (but cooled with a cooler) to maximize cylinder pressures for maximum fuel economy. One way to get to the 54.5 MPG (test cycle number - actual real world fuel economy would be about 39 mpg) is to do what Ford does with its Ecoboost engines that use cooled EGR and force it into the engines to get the maximum cylinder pressures for best fuel economy. If the EPA would push harder for higher octane base fuels in the U.S. like in Europe, for example, it would be a lot easier for manufacturers to meet the 2025 fleet standards. I do not recall if your EGR system on your 1976 440 has a vacuum amplifier to run the EGR, but I would not use that device since they are not durable and are problemattic. I would just run the direct ported EGR valve by teeing into the distributor vacuum port on the carburetor. With a smaller valve, you don't need a vacuum delay device and using one would not help off the line low speed spark knock that you would need to address if advancing your timing. I would never do without vacuum advance on any street engine by the way, as doing so just hurts fuel economy and increases exhaust temperatures and leads to early valve problems (I only mention this because I have seen a lot of guys get a performance Mallory or other distributor and run their street engines with no vacuum advance - it is one of the worst things one could do). But I know you are knowledgeable enough to not do this in any case.
