Hi Dave
Looking again through the NMRA spec, they set the size of the boards at 610mm wide and 1220mm long which fits the supplied sheets exactly! Is that correct? and we stay within the standard adopting their size!
A sky-board or back scene board has not been shown on the drawings above- minimum = 200mm, nominal = 382mm as per NMRA. Though I reckon we should have a minimum, but some layouts may need a board higher than 382mm to compliment the scene?
murrayec