The carbs would have to be set up to idle on both carbs if mounted sideways, or use an open spacer.  Since he is asking about a Thunderbird, I did not suggest using an open spacer.   The 257 does have a divider in the middle of those pads.  The divider goes directly through the hole drilled for vacuum to allow vacuum to be pulled from both planes.  Joe-JDC

JDC

Do you see any issues with my O/D using this setup?  I do not utilize the O/D kick down switch.  It's in the car, but I do not use it.

Type of trans has little to do with it other than an AT with a modulator valve with low signal.

Review this regarding side-by-side H-D-4 throttle linkage kits, it should provide basic understanding of the system-

https://www.jegs.com/i/Weiand/925/4025/10002/-1

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This is the linkage used with Edelbrocks.
https://www.speedwaymotors.com/Edelbrock-7094-Dual-Quad-Carburetor-Linkage,26823.html

  Vic Correnti

Thanks for the info.  I should get the manifold in the next two weeks.  I'm leaning toward the Edelbrocks. Two Holley 4Vs seem a little overbearing on a Y block and the linkage is complicated.  I really don't want to deal with 60 year old carbs.  Been there, done that.

I'm leaning toward the Edelbrocks.

I would lean that way also, even though I am not an EDEL fan. They will make for a nice street engine (IMO only) and look nice when the hood is opened.

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I keep coming back to the use of two Holley 2Vs?   I have never seen this setup, but it could look great with a custom oval 427 style air cleaner. I agree it's not vintage 50s hot rod, but to an old FE guy it looks great. 

Drive ability should be responsive.  You  wouldn't need complicated progressive linkage and the carbs are readily available.   Would turn some heads on cruise nights and start a lot of conversations.  If you used two center pivot Holley 2Vs, you could call it a 4 pack! (no bumble bee stripes please)

Obviously you would need to use adapter plates. Would the 2V carbs and adapters distribute fuel correctly to the 4V holes in the manifold?  Would any modifications be needed to an Edelbrock 257?

Sorry, I just don't see it, especially on a mid-fifties engine.

Maybe something like this was popular for roadsters before 4V or multi-carbs intake manifolds really came out.

A SGL 4V would be much more efficient. You will be working off two accel pumps and idle circuits. So much for fuel economy.

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On the Holley 2V carbs, the pump cams and discharge nozzles are easily tailored for a reduced accelerator pump shot.  You would likely need to custom make the carburetor adapters as you would be adapting from a pair of small flange 4V intake patterns to the larger pattern 2V carburetor patterns.  Intake manifold modifications would not be required.  I’m not aware of any adapters like that being commercially available but I don’t picture them being that difficult to fabricate with some basic metal working skills.  Fuel distribution would be the same as running dual quads so it would not be a issue assuming the throttle bores are all matched up accordingly.  To give an idea of how easy it is to make an adapter, here’s one I made to allow the use of a Holley 4000 4V carb (Teapot) on the later model large flanged 4V intake manifolds.
 

Lorena, Texas (South of Waco)

Thanks Ted.  Would you advise using two 500 CFM Holley 2V carbs or something smaller?  What do you think of this setup for a street driven mostly stock engine?