You will be best to create your own box, and Dixkert's #66 is very simple, reminiscent of the wooden butt trap. I suspect that box opens from the end of the toe plate as a lot of BC lids did. I see no button on the top, or on the butt plate. It is possible it simply snaps shut like a clam shell under the tension of a hidden spring too, but the toe plate tip flexing is more likely. Melchoir Fordney, a late Lancaster builder, used a similar device where the middle of the toe plate was narrowed and a cavity cut beneath, so that my pressing on it pushed a rod up and disengaged the latch.