The standard size element being used on the Tbirds is 1/2"OD smaller than the factory original. I think the element might be for many of the Ford engines that got the enclosed units with the snorkel.
 I just think it looks terrible with the gap around the edge on the filter base. On top of that the ID is also larger(which you don't see) which would reduce the paper surface area that the engine can draw air through, possibly creating a restriction. 
I'm surprised there is no correct element for the early birds with the number of them still around. 
I have researched and found an air filter size that is 1/2" taller than stock but with the correct OD, though still with a larger ID than the original Tbird unit.
I spent last night playing with Playdoh in the workshop with a torch in the engine bay so I could see through the bulge grill. To my surprise most of the filter lid falls inside the hood bulge. The only places where it extends beyond the bulge are a small part of the radius to the left and right of the carburettor. The closest it gets is 15/16" away. In fact it would almost fit completely inside the bulge if not for the extended rim that they put on the Tbird filter lid. I'm not sure what reasoning was behind the extra lip on the outer edge. 
What are the thoughts out there on how close the air cleaner lid can get to the hood? 

If you are referring to a 57 BIRD 4V, the original FORD P&A No. is B7SZ 9601-A.

SCOTT DRAKE offers a true replica-

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I think that WIX has a size match - but it doesn't have the perforated tin guard....... Will have to hunt down the number. I found one in Tucson the last time I looked - but only one - the usage is so slight that most auto parts place don't keep any inventory.

 
 Steve Metzger       Tucson, Arizona

You could put one of these air filters on your car.  Here's one on my TBird.  These were popular back in the day.  Fits right in the hood scoop.

I believe this to be the correct filter size and part number: 10.81" ID - 13.69" OD - 2.12 high B7S 9601-A    
The 13.3"OD is available through most filter suppliers but is too small. It may have even been later superseded (code for it is not correct but it will still work so put up for it) by Ford for that size.
From what I have seen from old images the original filters did not look like that. I think that is for Mustang.
I'm not after the original looking element as that is impossible to find, just a better fit. It appears the original filter had vertical and horizontal wire.
The reproduction hipo289 element might be close in height and OD.
Another thought is reducing the height of the 1/2" spacer under the carburettor but how would that effect engine performance? Maybe I should start a new post for that question.
The original question still stands. What is considered too close to the hood?

Too close has a lot to do with the condition of the motor mounts and steady rest. What I’ve done on more than just the bird is put the clay or playdoh on the a/c and go make a couple hard starts and full throttle pulls. Then measure the resulting clearance with the engine at full movement. I’ve run as close as 1/4” using that method.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

The spacer helps to insulate the carburetor from engine heat.  It also helps with power and torque and a taller one tends to be better.  So best to leave it in place.


Lawrenceville, GA

I think this is the matching WIX part - for the '57 air  cleaner. I collected up the stuff to fit one on my '56. WIX #42063.
Just holding that one as a "spare"......

Sealed this one to the hood - and it just fits into the scoop bubble. Too much heated air is ducted right off the radiator into the carb otherwise.

Got a cheap pitted hood grill off ebay  - and modified it - and eventually re-plated......oval air cleaner is just barely visible.


 
 Steve Metzger       Tucson, Arizona

Just a point for you Thunderbird guys since the thread is about air filters.. Remember to have a nut locking the stud at the carb top and do not have too long a stud. Last week at a Saturday get together I go to the were 2 Birds with a ding in the hood and paint cracking..... Happened a good friend too. I just hate to see that...

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

CORRECTION-

Original PN was B7S 9601-A and was replaced by B7SZ 9601-A. Both had the same dimensions.

This repro is not size correct -

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