Not only are drawings of coach No1 scarce, the information surrounding is vague. Boyd, normally very detailed, is quite general:
‘Spooner required... (1864) one first class and two third class... Bodies were 9ft.3in. over sides (and 10ft over bowed ends)long, 6ft. 3in. wide and where roofed(?), 6ft.6 in. from rail... the floor was only 8 in. above the rail...1st class bodies had two windows per side, flanking a central door... single back-to-back seat.’ Boyd F.R. vol 2
This fits the plates 11R and 12R. The earlier in 1887 show the coach open sided, the later from 1932 with the mesh added. But at no point in the text are the corresponding numbers mentioned.
With that information, vague though it is, it should be possible to sketch out a build drawing.