As of October 2020, most of the balsa X 31 model exterior is complete. It still needs window glazing and side mirrors, and the connection hoses which hang from each end of the loco near the couplers. The lights will probably be LEDs; the interior of the long end has lots of room for a battery and perhaps an electronic sound module and speaker to play the loco engine sound.
The inside of the cab is yet to be started. This will be modeled in Lightwave and 3D printed. Since the balsa roof is not permanently fixed, the 3D printed interior will be lowered into the cab. Thanks to the X 31 being on display at a Seymour Railway Heritage Centre open day a few years ago, I have an abundance of photographic and video reference material.
Unlike this model, the actual X 31 is not normally a static display. Since restoring it, the SRHC leases it out as a working locomotive to various freight companies. During October 2020 it has been seen hauling cement wagons on the Dandenong line, still in its Royal Blue and Yellow Victorian Railways livery.
The X 31 is just over 18 metres long. My balsa model is 1:20 scale and is about 920 mm in length from coupler to coupler.