Having made note of Mike's recommendation for these parts I have concluded that the parts supplied in three pieces in the current kit are not suitable to mount atop of the Sax boards the two cleat parts have a flat slab side made to suit the kit assembly instructions rather than a tapered edge.
Still I find that if fitted as per the manual they will sit too low and thus require too much material to be taken off the sax boards.
My personal solution is to fit a spacer beneath as a compromise, the sax boards will then be carefully mitred so the musetto looks like it is on top.
I began by filing the mating surfaces of the three parts before using CA so secure them as one.
I then marked the deck outline for the spacer
Some scrap deck
I am doing most of the pre shaping of the underside before assembling them as separate pieces.