Clif makes a lot of good things. Clif Gel Blocks are not one of those things. Even for hiking they're atrocious, during a marathon sounds significantly worse.
Congratulations on the finish in a very respectable time! Let us know if in a close few Pubski's from now if you'll be running another one. What kind, if any, of other workouts were you doing beyond the long run? Tempo, intervals, etc?