This is not a Hawaiian related entry....
In all accounts, the true precursor design of the reverse side of the Kennedy half dollar is from the Class 5 Kennedy President of the United States (POTUS) special Government medal (sGm). You have to remember that this Class 5 medal was struck while President Kennedy was still alive.
The precursor proof is the placement of the designer's initial "FG" (Frank Gasparro) in a familiar position (see video at time 1:38).
This was one of the most interesting historical facts I uncovered in my research.