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What you and Paul posted is simpler, if they are OEM rockers. In my case, I have aftermarket 1.6-ratio rockers from Rocker Arms Unlimited.

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These are the numbers  on the rockers  for factory rocker arms.
EAN - 54 /55  1.43
ECG 6564 56 and 57 1.54  ((56 jam nut, 57 self locking)
5751066 58-64 1.43
The ones you have most likely are aftermarket or a Ford replacement, most likely the  1.43  The difference in the two is the gap between the adjuster and the casting... 1.54 is 1/4 inch, the 1.43 11/32

This is from info i got from ford-y-block.com (Mummert)



54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Are you going to personally rebuild them or have somebody else rebuild them? You can measure from the center of the bore to the adjuster ball and from the center of the bore to the pad to determine the ratio. If they are original rocker arms, it's possible that no 2 will be exactly the same. 

I have a set of y-block rocker arms that came off of a 312 engine that I bought. The previous owner said he could never get the engine to run right. Since the engine has G heads and a B manifold, I believe it is out of  the 1957 Ford Fairlane. The rockers are not ECG high ratio. The only markings on them are the number 70 on the forward side and a random letter on the other. The letter is not the same from rocker to rocker, but the number 70 is. What I want to know is, what is the origin of these rockers and what is the lift ratio of them? I plan to rebuild these rockers and sell them if I can, and I need to know exactly what I would be offering, since I don't want to unintentionally mislead any potential buyer. Can anyone help me with information on these rockers? They appear to be in really good condition with hardly any wear, so they are a good project for rebuild. Thanks for any help!