This circuit board outline is consistent with the dimensions of official Z50Bus “Standard” circuit boards.
Official Z50Bus cards are normally made to the dimensions detailed on the Z50Bus webite.
While the Standard card height is 75 mm, other formats have also been suggested by Jon Langseth (developer of the Z50Bus). These include: Small (50 mm), Large (100 mm high) and Full (100 mm high and 150 mm wide). See here for details.