For anybody that cares to reproduce, the way I made this was to cut some scrap 2x4 in half, use a table saw to nibble out a notches with depth=thickness of bottom part of the rail, so it sits in flush, then I measured for the stays, did some trig, and came out with angles of 32/58 degrees (note 32+58=90). Probably 30/60 would also have worked, I would recommend do the trig first with 30/60, and let the resulting position of the bottom of the stays dictate the length of the 2x4 base.