Obviously, the side is a brass overlay - glued successfully using Bargs cement. Sometimes the cement gives way on such things as Walthers passenger car sides, but these relatively large surfaces seem to hold forever. Epoxy and clamps would also do just fine.
The wood is typically anything I have on the shop floor - usually construction wood, like "Western White Wood."
Laminating the block is with Weldwood water based exterior glue - never any problems.
Finish - multiple coats of lacquer based sanding sealer - I buy it in gallon form, but one can buy it an ounce at a time for model airplanes. Brush it on, let it dry, sand with regular sandpaper, and about coat #3 the wood grain is simply gone. Two more coats, then glue the sides on and shoot with your choice of locomotive paint.
This is standard for Walthers passenger car roofs, and I use it on any wood model, including those with scribed sides. I just do one coat on the sides, because I do not want to fill in the plank grooves. But for decals, you really want a very smooth surface.
For models, this is a lot like spar varnish. It seals against moisture, so you do not get cracks and splits after a long display period.
But, I had Lee Turner weather it and it was the most lifelike model I owned, until I stupidly sold it to a fellow in Dallas. 