Mark,
There is a lot about your original post that made me nervous. It’s excellent you now have bees, but acquiring bees in a used box like this can be very risky with regard to diseases as you don’t know why the original colony absconded. Another concern is that the colony that has taken up residence is small, which may not be an issue (ie. secondary swarm), but you should keep an extremely close eye on the brood that this colony produces for things like chalk/afb/nosema as it may be staying small because of a disease latent in the wood ware.
Are you able to take photos of the frames that the bees aren’t building in? it would be interesting to see why they prefer to build off the bottom of the frames. Are there any signs of old wax/moth/beetle on on the frames? Make sure when you cut/rubber band the comb that you place it in new frames with known provenance, and rotate the old frames out as soon as practical (ie. let the brood hatch from them, then swap in new frames).
Some photos of the rubber banding process here (sorry to post again for those who have seen them!):
-edit- Just saw Dawn’s thread… looks like rubber bands are the same the world over 