The ogam script is considered to be early sixth century, but the cross could
have been carved at any time after, or much later. The cut marks seem
somewhat 'fresher' then the ogam.
(Early medieval Munster: archaeology, history and society, Michael A. Monk,
John Sheehan, (1998) pp.29-29)
Perhaps this would be helpful...
Devane, Caitríona: An Ogam-inscribed stone in Ballintaggart
In Peritia 15 (2001) pp. 369-372.