OK, I understand the problem.
You want to put a std. Tuttle fin in a Deep Tuttle fin box.....correct?
For this you need the 90 cm screws as from the original Larry Tuttle Drawings, the
Deep Tuttle is 17 mm deeper than the Std. Tuttle.
So, check with your nearest Starboard dealer or windsurf shop.
They should have the 6 mm x 1.0 x 90 mm fin screws you need.
They are available, just hard to find.