Tom P. Thanks for the pointer, I should have remembered to go there. On page 265 of my copy (The Classics of Golf edition) CBM says how the 1.62x1.62 became standard for both associations in May of 1921.
CBM also says the Americans wanted the heavier ball rather than the floater, which the R&A was "more or less in favor of" and yet 5 years later the positions had reversed. On July 23, 1926, the New York Times ran and article stating that WC Fownes (then President of the USGA) and others had returned from Britain and were unable to get the R&A to go along with the proposed change to a floater. Fownes is quoted as saying, "There is a general impression that the larger and lighter ball, such as we adovcate, would curtail length." He also says that the USGA had been arguing this for 2 or 3 years. So even as early as 1923 or 1924 the positions were reversed from what CBM states above.