Numbers in 'igh-up positions (6)
I believe the answer is:
eights
I believe this is a double definition.
'numbers' is the first definition.
(eight is a kind of number)
''igh-up positions' is the second definition.
('heights' said with a cockney accent, dropping the 'H', like 'high-up positions' was)
'in' is the link.
(Other definitions for eights that I've seen before include "Boat race crews" , "Rowing boat race, eight eight" , "Numbers for rowing crews" , "88888" , "Sets of rowers" .)