I've been considering building one of Tom's designs, but I wanted a proper masik in it, rather than a frame. I think I have a reasonable idea of how to do it. It would entail cutting out the top section of the frame, but keeping the attachment points for the gunwale stringers, creating a roughly U-shaped "3/4 frame". Next, fabricate a masik (I like to use 3" wide, steam-bent oak) that's 1/2" thicker at the ends than the diameter of the tubes (if you're building an aluminum tube folder), or equal to the thickness of wooden stringers (for a wood framed boat). For a tube frame, you would cut/rout a groove in each end to fit over the gunwale tubes, then cut a notch in the center of each end to fit around the 3/4 frame, straddling it. For a wooden frame, you would just cut the masik to fit between the stringers and cut a notch for the 3/4 frame. The masik would be held in place with pegs or screws through the stringers.

Does this description make sense?

You can see pics of the masik style I prefer at the link below, in my "Steam Bent Masik" album and those for my boats. That might give you a better idea of what I have in mind.