I have several concerns. First, 1,600 CFM is no where near enough for a stand alone electric fan set up. If you aren't going to move at least 3,000 cfm you're not setting yourself up for success.
Second, the 4 core radiator. I won't get into 2 core vs 4 core or any of that crap as far as cooling, most of all that is gimmicks vs science anyway. But, A-bodies don't have a ton of space to work with, and if you make the radiator too thick you'll run out of clearance to the pulleys. A 4 core will be difficult to deal with for setting up the fans because of the thickness of the radiator.
I run a 26" 3 core Champion radiator with a '95-'00 Ford Contour dual electric fan set up on my Duster. It has a built in shroud, which is important because it means the the rated CFM for the fan is more likely to be reproduced for your application. With a non-shrouded fan it's almost impossible to tell how it's rated or if you'll actually see that CFM in your application. The CFM numbers are roughly 3,500 cfm on the low speed, with over 5,000 cfm on the high speed. It's pretty rare, but I have had the high speed kick on while I was in traffic in 100°+ degree weather. Which means, if I hadn't had it, I might have been on my way to overheating. You need more CFM than a lot of aftermarket fans are capable of to cool a moderate 418. The Contour set up is a very capable fan set up, Ford was nice enough to test the living crap out of it, and the reproduction fan assembly is made by Dorman and is cheaper than any of the aftermarket fans capable of moving enough CFM.
My install on my Duster is here
My "new" '74 Duster- or why I need a project like a hole in the head
And the set up looks like this. You can see there isn't a ton of clearance even with a 3 core, and the Contour fan set up is relatively thin for a standalone electric fan.
View attachment 1715492151
View attachment 1715492152
@goldduster318 did a very nice write up of his install of the Contour fan set up with the Dakota Digital controller, I basically followed his install when I did mine. The PDF he did should be attached at the bottom of my post...
A well designed shroud adds to the capability of the fan. Without a shroud, the fan will only pull air across the part of the core that it covers. With a well designed shroud, it will pull air across the entire core. If you're not pulling air across the entire core you're losing a ton of cooling efficiency. Not only that, but fans are pretty much always tested with some kind of shroud. So without one you can pretty much guarantee you won't get the fans full rated CFM.
As for the "blocking air" thing- if the shroud is on the backside of the radiator, it's not blocking air. The air has already passed through the core at that point. If the fans are small and the shroud doesn't allow all the air to pass easily through it may reduce airflow through the engine compartment, which will also reduce cooling, but it doesn't reduce the airflow through the core unless it's out in front.