Pl search our archives for udayarkudi. It mentions of the assasins is the tamil word throgigal ( traitors) and not abauthuvigal. That part is kalki's work
The udaiyargudi inscriptions clearly show that a group of brothers were involved with the murder. And there are many circumstantial evidences that to point their chera affinity. (I've mentioned them in the course of the novel)
How chearas were involved with a sworn enemy of pandiyas (i.e. Aditya) is indeed an intriguing question.
Similarly the historic Uttama chola is quite different from the character which we meet in PS.
My novel, as you know, is more about kanthaloor chalai events rather than the murder itself. But these details provide a backdrop.