It is interesting that the part number in my 56 and 61 books are the same.
Chev sometimes will use the same casting number for two parts that end up being machined different, but I have never seen the same part number used even if there's the slightest differences in the part.
Rockers would have no effect on compression ratio, it only has to do with how much volume in the cylinder is being squished into the cylinder head combustion chamber.
