My "1965 Ford Service Specifications For Cars and Trucks" (First Printing) is dated September 1964.
(Cars) - Engine ID - Warranty Plate symbol:
"L" is for overhead cam 427 V-8 (4V)
"M" is for 427 (ohc) 8V
(page copy attached)
Q: WHAT were they THINKING?
That is the book I saw at Mr. Rummels shop. Thanks for posting it