At the Oshkosh MARC national meet this year, someone brought in a restored Model A prototype chassis that was built in mid-1927. It has a lot of design changes from the production cars. No records were kept of why one design made it and the other didn't, but we do know that the prototype used expensive shock absorbers that weren't going to cut it for the production design. According to Bob Martino, who restored the prototype, "Ford worked with... Houdaille to design a much less expensive shock.... In July & August of 1927, the chassis and suspension had to be redesigned to accommodate these shocks."
I mention this because the prototype uses rear motor mounts that look surprisingly similar to the FAM mounts. I wonder whether the design that eventually became the production mounts was preferred because of the need to design around the cheaper shocks.