Thank you both, much appreciated.
I can't move one of them at all, but the other definitely opens. I think I'd better glue it.
It has other issues - missing nut holding the three-way switch, woodscrews and washers holding the strap (!!) (those went ASAP, but I will probably have to plug and drill the body to put sensible strap pins on), a nasty crackle on two of the switch settings, the switch endcap is missing, and quite a few dents bumps and bangs. So I may well wind up stripping it for parts.