Hoping for help Identifying Fin Box on Hobie?

I’ve been working on restoring what I think is an early 1970’s Single Fin 6’2" shortboard that came without a fin, but still has the box intact.

Any clue on what will fit in this box?

I’m attaching the only photo I have at the moment…sorry its small.

You might want to try another photo. That one is so small and dark it’s impossible to venture a guess.

I know sorry…I don’t have the board at me at this time, but will try to snap one in the future…I gotta get this thing finished and in the water.