The United Arab Republic failed because Nasser's Egypt effectively treated Syria like it was a vassal state, not a equal Arab state. Nasser demanded that all political parties in Syria be banned and attempted to form a centralized authority based in Damascus for one half of the year and in Cairo for the other half of the year, abolishing all regional governments in the process. This dominant attitude from Nasser effectively created the idea of Syrian nationalism, which slowly built up popularity until the military overthrew the UAR-aligned government in 1961.
At that time, there were more plans about subdivision of hypotetical united Germany. I found about Gustav Struve but am not able to find map, however it should contain: Upper, Middle and Lower Rheinland, Svabia, Franconia, Hesse, Vestphalia, Thuringia, Upper and Lower Saxony, Schleswig-Holstein, Meklenburg, Brandenburg, Prussia, Pomerania, Silesia, Bohemia, Moravia, Bavaria, Austria, Styria, Tyrol and Illyria (maybe otl Ilyr kingdom, with Terst as capital).It isn't so bad. Thuriginia and Saxony had some overlap with names and territory in the past, and the Ernestine and Albertine Duchies were called Saxony at various times. There is a Saxony here already, so they gave the other the name of Thuringia. Might be ways to explain the Palantine part as the Wittlesbasch consolidating their various dynasty lands there, and the Prince-Bishoprics, though as those were straddling the rather than being in one side, it does indeed not fit here. Heck, I think the that much of the Rhine was only ever a border when the Entente were occupying it, and even then there were a lot of cities occupied on the far backs. Well, not counting during the First Republic.