Managed to free the Meson centerboard at last.Drawing here.
It's a picture of the drawing. Draw a 50 X 50mm grid on a sheet and reproduce your own real size original.
(1) This is a copy of a Meson Centerboard. I think it's identical to the Sprint II, but recommend to make a cardboard version first to verify. Let us know if it does fit please.
(2) The thickness of the Sprint centerboard is 26mm (2 x 12mm + coating?).
(3) Measure the width of the slot for the king pin according to your setup.