Hi Dennis, for what it's worth here's a way to make the process more complicated. 1/2" on either side reduces what already is a tight fit for my size 11 ft. A simple solution is to use 4mm ply, cut the tabs down enough, glass the 4mm with 2 layers 9oz tape then install the nuts,eeek with half the wood removed for the recess. For an even more over board way to make the nuts flush, cut the tabs off, lay 4 2" strips of unidirectional carbon over the t-nut then install with a piece of plastic covered ply(temporary for making the goopy carbon flat) between rails and carbon. Oh and holes need to drilled through the threaded part of the rails with a screw (allen is easier to install) holding the rail on.