At one time the 5752-113 cylinder heads were the Ford replacement units for the ECZ-G units. This info is on John Mummert's web site
http://www.ford-y-block.com/cylinderheadchart.htm and I've seen it somewhere in documentation from the Classic Thunderbird Club International. -Probably in the C.T.C.I. Thunderbird Restoration Details and Specifications Manual.
Because they are the FoMoCo designated replacement part for the original large letter ECZ-G heads, my understanding is that you would not even be penalized points in a C.T.C.I. Concours judging event.
Per John Mummert's web site, ECZ-G cylinder heads were not 'posted' until beginning May of the 1957 model year. While the 1957 'Birds continued to be produced until a date in early December of 1957, there are a lot of little 'Birds with non-posted ECZ-G heads. ALL 113 heads are posted. Other than casting marks, the only significant difference between the 'G' and 113 cylinder heads is the volume of the combustion chambers. Per JM's web site, 'G' heads are 69cc while 113s are 72 cc.
In stock trim, info on this Forum indicates that 113 cylinder heads flow better than 'G' heads.
While the 'G' heads have long been heralded as the heads to use in building a y-block engine, I prefer the 113 heads because there appears to be less combustion chamber shrouding around both the intake and the exhaust valve in each chamber.
Hope this helps.
a.k.a. Charlie Brown
near Syracuse, New York