G'day Andy,
Just going back to your difficulties with assembling the Signal Box, I presume it's cast in Polyurethane. If so, the only successful adhesive, other than contact adhesive, is Superglue ( Cyanoacrylate ).
I've been manufacturing model railway kits and accessories in Polyurethane for over 25 years, and my recommendation is to roughen or abrade the faces of the joints to be glued. This can be done with emery or similar, or scraping with a knife blade or file.
After doing this the superglue will/should go off very quickly, whereas if not treated this way I have found that the superglue will not go off at all.
I have found that even the cheap superglues will work well after this basic preparation.
Ian Storrie
Ian Lindsay Models