Moment heavyweight unit was top of the heap (6,2,4)
I believe the answer is:
second to none
'top of the heap' is the definition.
I know nothing about this answer so I can't judge whether this works.
'moment heavyweight unit' is the wordplay.
'moment' becomes 'second moment' (second moment is a kind of moment).
'heavyweight' becomes 'ton' (a ton weighs a lot).
'unit' becomes 'one' (synonyms).
'second'+'ton'+'one'='SECOND-TO-NONE'
'was' acts as a link.
Can you help me to learn more?
(Other definitions for second to none that I've seen before include "perfect" , "Incomparable" , "certain champion" , "Unsurpassed" , "Pre-eminent" .)