Rock Edict 13 has
And it (conquest by Dhamma) has been won here, on the borders, even six hundred yojanas away, where the Greek king Antiochos rules, beyond there where the four kings named Ptolemy, Antigonos, Magas and Alexander rule, likewise in the south among the Cholas, the Pandyas, and as far as Tamraparni. (transl. Dhammika)
A bit closer to the original orthography is Siracar’s edition:
And such a conquest has been achieved by the “Beloved of the Gods” not only here in his own dominions but also in the territories bordering on his dominions, as far away as at the distance of six hundred Yojanas, where the Yavana king named Antiyoka is ruling and where, beyond the kingdom of the said Antiyoka, four other kings named Tulamaya, Antikeni, Maka and Alikasundara are also ruling, and towards the south, where the Codas and Pandyas are living, as far as Tamraparni.
“Yavana” is an old name for Greece, even today “Yavan” means Greece in Hebrew and similarly in other languages (link)
Oskar von Hinüber footnotes in his 2010 paper “Did Hellenistic Kings Send Letters to Aśoka?”:
The names of these Greek kings were discovered and identified as early as 1838 by James Prinsep (Hultzsch, Inscriptions, per p. xxxi). This famous and well-known passage is used to date Asoka to that time when the reigns of the Seleucid Antiochus II Theos (261—246) of Syria, Ptolemaeus II Philadelphos of Egypt (283-247), Antigonus Gonatas of Makedonia (277-239), Alexander of Epirus (272-256/255) or of Korinth (252-244), and Magas of Cyrene (dead before 250) overlap.
In his paper “The Diverse Degrees of Authenticity of Asokan Texts” Harry Falk doesn’t mention RE 13 as in any way doubtful.
Also Guruge in his chapter of Seneviratna’s 1994 “King Aśoka and Buddhism” has no doubt about the kings’ identity:
They have been identified and dated with a fair degree of accuracy as follows:
Antiyoka (also mentioned in RE II): Antiochus II Theos of the Seleucid dynasty in Syria and West Asia (i.e. the immediate western neighbour of Aśoka’s empire): 261 – 246 B.C.
Turamāya (Tulamaya): Ptolemy II Philadelphus in Egypt: 285 – 247 B.C.
Antikini (Antekina): Antigonus Gonatas in Macedonia: 277 – 239 B.C.
Makā (Magā): Magas of Cyrene in North Africa: 282 – 258 B.C.
Alikasundara: Alexander of Epirus: 272 – 255 B.C.
Even though he has a subchapter on “Historical Reliability of Rock Edict XIII” he doesn’t conclude any doubt int its authenticity.
Gombrich in the same volume also relies on the names and dates. He writes
The kings, all of whom ruled in the Hellenistic world, the Near East, have been identified; from their dates we can deduce that the inscription was dictated in 256 or 255 B.C., and this gave modern scholarship the key to dating not merely Aśoka but the whole of ancient Indian history.
A Greek version of RE 13 was found at Kandahar in 1963. Unfortunately only its beginning (without the kings’ names) survived.
So all in all there seems to be no doubt in the edict, the identification of Greek kings (with the exception of which Alexander is meant), or the dates.