gun fin & fin placement

Does anyone have suggestions for an appropriate fin for an 8’2" single fin gun (N 12 3/4, W 20 1/2, T 12 1/2 round pin, lots of v; sort of a puffed out Parrish template…)? And where would you place the fin?..Currently I’m using an 8.5" Dale Dobson (Fins Unlimited) which works great in my early 70s G&S Magic. I’ve got the fin 7" up in the gun. Is this fin appropriate? How about the placement?

c’mon,please help…

With a 12 1/2" tail you’re probably in the ball park with the 8.5" Dale Dobson fin 7" up. If it feels too stiff, move it up in increments - too loose, move it back. Ride it and figure out where all the “buttons” are.