Green’s Dictionary of Slang

top tens n.

[rhy. sl.; top ten hit = tit n.2 (1)]

(Irish) the breasts.

[Ire]P. Howard Miseducation of Ross O’Carroll-Kelly (2004) 60: The sly little little look he has at her top tens.
[Ire]P. Howard Curious Incident of the Dog in the Nightdress 6: She’d no top tens as such. [...] I’d bigger pecs.