Blocky. In the U.S., FoMoco y-blocks were principally manufactured for car / truck use from 1954 - 1964. It's been indicated that marine y-block applications went produced for somewhat longer into the later '60s. The early, first year y-block heads had some production variations from those produced late in '54 and on up. What I can't recall dates for is the years of y-block production in South America. Argentina, I think, for one.
Many parts, but not all, interchange '54 - '64. To be safe, figure that 1955 through 1964 cylinder heads can be interchanged. As a rule of thumb, it's best to replace them as same year sets due to variations in combustion chamber volumes and intake valve size. The number of different series of heads used over the years is amazing to me. In the early years, ('55, '56) it intrigues me that the compression ratio used on the auto trans engines was higher than on the standard transmission engines. -Yes, different size /shape combustion chambers were used on one transmission application versus the other. FoMoCo seemed to stop worrying about that by 1957.
John Mummert's web site listing of y-block cylinder head applications may be of interest to you if you haven't seen it.
Click the link below to view JM's FoMoCo y-block cylinder head application listing.
http://www.ford-y-block.com/cy...Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York