I have three field cameras that take Technika boards and two others (monorail and field) that take 4x4 lens boards. I have made an adapter out of Masonite so I can use the Technika boards with my Zone VI field camera and my old Graphic View (my Sinar has a Technika adapter board).
What I did was to make a 4x4 piece of 1/8-inch (or 3/16-inch... not sure now, but the thickness needs to match a factory board) Masonite that fit the cameras with 4x4 lensboards. I then traced the circle of the extended ring on the Technika board onto the Masonite piece and cut that out resulting in a 4x4 board with a large hole in it. That was the easiest part.
Next I laid the Technika board into the hole (which I filed out a bit so the Technika board would lie flat) and marked the outside dimensions of the Technika board onto the Masonite board. There is just a bit; a tiny strip, on either side that is actually exposed when the Technika board is in position. Then, with a sharp knife and a metal straight edge, I scored the lines on the Masonite board and carefully peeled, whittled and chipped away a recess that the Technika board could nestle in. The object is to get the Technika board flush, or very nearly so, with the remaining surface of the Masonite (just the little strips on each side). The result is a thin 4x4 Masonite board with thicker edges and a large hole.
Once finished, I "finished" my Masonite boards with black Sharpie. The "adapters" live with the cameras. When I want to mount a lens on a Technika board, I pull out the adapter, sandwich the Masonite adapter and the Technika board, and mount the whole thing as a unit. All is held in place with the sliders/metal slots, just like a regular 4x4 board.
I've used this a lot, even with recessed Technika boards, no light leaks ever. So, if you're good with a pocket knife and hand tools, you can make yourself an adapter.
BTW, my Masonite stock came from an old picture frame.