WOW!
I had one of these things.
Mine was nearly exactly the same excpt it had olive green bottom and rails.
I rode it with a 10" deep Greenough template fin and soon after added 4" base X 4" deep wooden side fins just ahead of the main fin.
It worked well.
It was the last spoon I ever owned.
One time the 10" deep fin struck the reef, while surfing low tide Acid Drop on Kauai, during a bottom turn and I got launched off the front of the board.
Another time, I nearly had my throat cut by the long deep single fin while surfing 4-5' Honolua Bay Maui.
(I still wear the scar under my chin.)
That ended the single fin era for me.