That... wouldn't make much sense for the scope of the mod. The Indo-Greek kingdom had been gone for at least 470 years at the start of the mod, and it wasn't really an important or remembered realm like the others that can be restored (WRE).
Just maybe like Mr. Capitalist says, make it the Greek name for Afghanistan.
Probably better to have the cultural name. I was not for especially but thought that the titular title was better than a decision for this since long dead kingdom. If the kingdom needs to have dejure provinces a titular kingdom is not a good idea.