Looks like the two 56 castings are the 2 different ones. Casting # on the top of one and the bottom of the other. The "8" shaped one also is flat where the carbs bolt and the other has indent/open areas between the studs unless one has be trimmed a bit. The 56 did not need an indented valley cover either as I understand it like the stock 57. Did any aftermarket dual quads need one?  I love reading and learning about these early factory and aftermarket performance parts.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Thanks Ted. There is a definate difference but to me its not enough that you would ever be able to tell in driving the car. Would probably show up on the quarter mile times but again i'm thinking not much. Driver could make more difference than that. I would still got for the stock .57. Not enough difference between the stock '56 to worry abour. The aftermarket manifolds would be an improvement though. I port matched my '57 to the heads but no idea how much if any help it was.

Here are pictures of a 1956 EDB manifold modified as you describe.  The four independent throttle holes have been converted to the kidney shaped holes as found on the 1957 ECG 2X4 intake manifolds.  This modified manifold was dynoed along with the other manifolds on an aluminum headed engine and it was down on power when compared to a stock EDB manifold.  Here’s the link again for the dyno test results.
 
Dual Quad Intake Testing

  

 

Lorena, Texas (South of Waco)

Got a question while we are discussing manifolds. I have a '56 manifold that has been modified by grinding out the divider so it looks like the kidney shape of the '57 manifold. I've been told that this has been apparently done a lot and signifantly lowers the price on these. How does affect the performance?

I was refering to Oldcomics2. Unfortunately what I had was not the one he was looking for.

Hi Slumlord
If you were referring to me re the manifold, I have one, but had no idea if there was a difference.
Now that I know my 57 type makes an additional 50+ Hp, I'm going to use it :-)
Thanks
Jim

Prety sure I have one if you are interested.

A little bit, http://www.eatonbalancing.com/2014/01/17/y-block-ford-dual-quad-testing-on-aluminum-heads-part-ii/


Lawrenceville, GA

Is there any performance difference between the 56 & 57 manifolds?
Thanks
Jim

Ted
I have been looking for that style of 56 manifold for a while now. Its only the second one that I have seen with the part# on the topside.Goes to prove that there were two different runs of the 56 manifolds

Like Hooser said most of them are cast with the part# on the bottom. If that manifold is for sale OR if you want to swap me for a bottom cast 56 style manifold - please let me know.
Thanks

Oldmics@Yahoo.com