In 1963 there were two conch shell shaped horns roughly 5" diameter. One Hi Note and one Lo Note. They were marked with the 'L' and 'H' inside the lip of the horn. The standard 1963 Hi note horn was originally part # 900-0444, but was then replaced with the smaller 1964 style Hi Note horn # 900 0514 as stock was depleted. The standard 1963 Lo note horn was originally part # 900-0429, but ws then replaced with the smaller 1964 style Lo Note horn # 900 0513 as stock was depleted.
There was also an optional Eldorado Style "B-Flat" note long trumpet horn offered in 1963. The part # was 199 9947, and stamped 947. It was standard on the Eldorado and optional on other body styles as a dealer installed option.
In 1964 there were three horns standard. Two conch shell shaped horns roughly 4" diameter...One Hi Note and one Lo Note. They were marked with an 'L' and 'H' inside the lip of the horn. There was also a Hi C-Note short trumpet horn standard on all body styles except the Eldorado.
There was also an Eldo Style "Low-C" note Long trumpet horn, standard on Eldorados, and offered as a dealer installed option on other body styles. The part # was 199 9896, and stamped 896. When this horn was installed on non-Eldorado body styles, it provided a unique 4 horn setup.
According to later Master Parts Book (e.g. 1969 MPB) the smaller 1964 style horn were used as replacements as needed for 1963 and earlier Lo and Hi note horns. In fact the Master Parts book shows these horns as being used for 1953 to 1969.
See 1965 Master Parts Book Scan below (click to enlarge):