i have the slinden book, and it only says "Incandescent gas lighting , with roof pipes, was fitted from new to those om Lots 1133 and 1162 and to the remainder in 8/09.
The only picture i can find showing the roof is on page 34 of Wild Swan Publications book of the Calne Branch by Colin G Maggs . it shows only 2 lamps.
Nice kit, must finish mine one day, been part built for at least 10 years, just needs the roof painting ,fitting, and lettering applying!