The Collaborative International Dictionary of English v.0.48:

Flong \Flong\ (? or ?), obs.
   imp. & p. p. of Fling.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Flong \Flong\, n. [Of the same origin as flawn, flan, a metal
   disk.] (Stereotyping)
   A compressed mass of paper sheets, forming a matrix or mold
   for stereotype plates.
   [Webster 1913 Suppl.]