While I have to work for stuff at the moment, I can snatch a little time for an update that might prove useful. Breaking the faux-history character of the timeline for once, I'm going to directly deal with the similarities and differences between TTL's Argead Empire and OTL's Seleucid Empire. I will divide this by topic to make it clearer to understand.
Argeads vs Seleucids Grudge Match!
Geographical Span
At its height, the Seleucid Empire controlled the vast majority of Argead territory, extending from Anatolia all the way to north-western India. The major differences is that by this time, the Seleucids had contracted considerably. The Indian satrapies, Bactria, Arachosia, and most of Anatolia had all been lost to various other powers or to rebellion. Additionally, Macedon remained an independent state and an separate successor state to Alexander's Empire. Malta, the westernmost possession of the Argead Empire, was never controlled by a Hellenistic power and passed directly from Carthage to Rome. Likewise, Arabia in OTL was not under the control of any Hellenistic state, although certain Arab states and tribes
were. At its height, the Seleucid Empire would have been almost as large as the Argead Empire, but in 200 BCE it was far smaller.
Administration
The techniques used by both Empires to run the Empire and control it are actually quite similar. In the Argead Empire Alexander V doubles the number of satrapies in order to reduce satrapal power, this was also done by the Seleucids (the precise timing of it is difficult to discover). The Royal Roads were used by the Seleucids in much the same manner as the Argeads, with the only major difference being that the Argeads extend the network to encompass more locations. Both Empires were run by direct monarchies with male succession, both almost certainly used a Crown Prince figure in administration. Tax collection, tithes, and levies are all arranged in a very similar manner by both Empires. The most major differences are that the Argeads are a little more assured of not relying on Greek-speakers to guarantee loyalty, and thus have founded less cities than the Seleucids; the resources have instead been spent on infrastructure for the state, such as large logistical forts larger than the equivalent in OTL Seleucid regions. But even at this point some of the basic realities of the two Empires are similar, such as the physical shapes of coins/currency forms and the design of buildings and cities. The Argead Empire simply has more resources to throw at problems.
'Hellenistation'
This is a harder question to answer because of the difficulties of determining how Greek culture spread in OTL. The use of Greek as a prestige and vernacular language is just as strong in the Argead Empire, but the cultural process of Hellenisation is actually both weaker and stronger than in OTL. It is stronger in that Greek culture has been more successful with peoples historically resistant to it, but weaker in that the Empire has also ensured the spread of its non-Greek cultures across a wide area. The literary boom in the Argead Empire has been responsible for transmitting Greek culture east, but also Asian cultures west. It's not just a question of Persians Hellenising, but also Greeks Persifying (for example). There is evidence I'm more familiar with than I was before about Hellenising in the Seleucid Empire, including examples in Uruk of all places. It can be said that the Imperial culture of most of the big Near Eastern Empires tends to get aped by the elites of the territories they control; you even get examples of Assyrian-style goods being produced outside of territories Assyria directly controls in the 8th-7th Centuries BCE, so this sort of thing has a long history. Since this process is working both ways, expect a few
new cultures to eventually get created by the Argeads by the mixing of older ones.
Religion
You'd think I'd changed a lot about the religions of the world, but you'd be surprised. Alexander cults did actually exist, although their rituals are unknown to us. Indeed, ruler-cults in the Seleucid Empire begin to sporadically emerge pretty much spontaneously, so their absence is one of the few things I've straight up added/removed from history. Buddhism spread quite far into Arachosia, so all that's happened is that the Argead Empire has had a deeper contact with the religion and the areas interested in it have increased compared to OTL. In general, all that has been done is that the influence of certain religions or practices is increased or decreased compared to the Seleucid Empire. The creation of 'state' cults like the official Alexander Cult of the Argead and Ptolemaic states is also true of OTL history; the Ptolemaic state of OTL created the cult of Serapis in order to lubricate social cohesion between Greeks and Egyptians. What this timeline is seeing is an accelleration of some of the social processes leading to religious evolution; the Alexander Cult is in many ways similar to the Imperial Cult of Rome around the time of the Julio-Claudians, the major difference is that this Cult has a set dogma and is officially moderated from the very beginning by the state. In essence then, the Seleucid Empire was a crowd-pleaser whereas the Argead Empire is both a crowd-pleaser and a religious innovator. This is perhaps the most major structural difference between the two states.
Military
The area with the least difference to OTL between the two states. Both states rely upon a combination of Macedonian phalangites, professional units inherited from the previous state, levied units from cities and satrapies, and mercenaries. Both the Argeads and Seleucids recognised the value of heavy cavalry when they encountered it, and developed the kataphractoi. The only real difference is probably that more non-Macedonians have been trained in phalanx warfare by the Argeads than the Seleucids did. Ironically, the Argeads probably also possess more Macedonian troops/cavalry overall due to their lack of constant conflict with the Ptolemies compared to the OTL Syrian Wars. In essence the Argead military is nearly the same as the Seleucid military but is simply larger.