Is there a Midnite GFCI device sized just right for the KID? (Or does he have to go around in his big brother's oversized gear? ;))
Well the GFPD can not be used for the Over current protection or a disconnect so the size really doesn't matter (Or ampacity wise it doesn't)
So you would go from the PV through the 63 amp GFPD and then through a 30 amp breaker into the Kid.
The issue is, If the GFPD is used for a disconnect or for over current protection then it ungrounds the negative when open and that is not a good situation so NEC says it can not be considered the disconnect