Ok I've had a go at a timeline (currently have it thought out in my head, still not sure how to work it out). This is the first part; please critique:
PoD; Greek vicotry over Cathaginians and Estrucans at Alalia in 540 BC. Securing the Greeks various Carthaginian Island terrorties and the Straits of Gibralta, the securing of monpoloistic trade in the North Western Med; blockade of straits to ensure greek monpoly over trade of Tin from Britian.
Carthage isolated to Malta, sicilian and African holdings. Estrucans lose out on trade, and are weakened by indemities. Strengthening of Greek cities (well, wealthier), also slightly wealthier Greek City states in Greece.
Subsequent defeats of the Estrucans in following decades truly reduces Estrucan power (Navies are expensive!)
Gauls migrationary tracks bring them into conflict with the Estrucans in approx 400 BC, weaker resitance gives a quick collapse of the Estrucans and easy victories and pillage for the Gauls means that the raids and settlements are further south than in OTL which
Brings them into conflict with the Romans; Rome is sacked not once, but thrice; severly weakened, the conflicts with the Samnites goes much differently.
343 BC: In the 1st Samnite war; the Samnites defeat the Romans in series of battles, ensuring that no compromise peace is made (Capua was joined to Rome as well as follows), and that the Romans recognise the Samnite union with the Sidci is recongnised as well as Capua being ceded to the Samnites.
326 BC: The 2nd Samnite war results in a compromise peace which sorts out minor terretorial issues and matters of infulence, the Romans were unable to block of Samnite routes of expansion as OTL.
298 BC: 3rd Samnite war; results in defeat of Romans at hands of Samnites, various colonies and cities ceded to Samnite infulence or control, Romans weakened.
280 BC: Samnites growing infulence in southern Italy forces it into conflict with Tarentum; who invite King Pyrrhus of Epirus. King Pyrrhus accepts and comes to Tarentum with a large army and war elephants. However the wealth and decadence of Tarentum has been heard of, and Pyrrhus enters the city and then deposes the current, decadent rulers, confiscating their estates and utilising the Gold for the war effort. Additional Mercanaries are hired; and Auxillary units from nearby peoples are utilised.
In subsequent battles Pyrrhus conquors the Samnites, losses are minimal as the armies extra size and the Samnites weaker armies put up less resitance.
By 275 BC Samnites are defeated and Pyrrhus is victorious. The Romans who had opportunistically taken some territory off the Samnites, when Pyrrhus demands these terrotries, the Romans refuse and war ensues; the Romans secure an alliance with Carthage (or what remains), who make attacks into Sicily and sends a force to support the Romans.
In 273 BC Rome is conquored after a costly battle on the Appian way; Rome unable to produce another sizeable army is destroyed. Pyrrhus then turns south and reconquors parts of Sicily in 272 BC.
In 269 BC the remaining Carthage holdings in sicily are captured, and with the dominance of Pyrrhus a Kingdom of Italy and Sicily is formed (name? any ideas?).
In 267 BC the remaining Carthage lands are conquored and incorperated into Phyrrhus's realm and By 262 the reamining Greek colonies in the Western Med have been conquored.
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In the West Med; Alexander took 3 years longer, due to having to knock some heads together in Greece (slightly stronger City States). This results in more direct rule in Greece for the Macadonic state (although not everywhere); however Persian internal problems sped up Alexanders conquests somewhat, and he was more or less on track near the end. (he died with similar results for the dissolution of the Empire).
Critiques? Still have some ways to go;
Anyone willing to give a name to Pyrrhus' realm? Also I DO note that the time period is unlikly to through up the same peoples, however I've simply deceided that similar personalities will be thrown up and just used them....