The center plastic bar is cracked on all the early 126 cars I've seen. Pieces missing on many. Couldn't get mine to hold with any type of adhesive. Even tried plastic "welding" with the old solder gun attachment. Doesn't seem to matter that much. Still looks nice when all together.
The brackets (great friend you got
) can be glued with a cyanoacrylic (superglue) gel and held with a medium spring clamp if the fracture is within the plastic itself. The only place I know to find them is from an old piece of console wood at a wreckers'. If it has pulled out the little metal "teeth" from the wood, then you have to get some E6000 Craft adhesive (Michael's) and work the glue underneath the bracket the press the "teeth" back into the wood and clamp. Use a towel to protect the finished side or you'll really get mad.
As far as putting the radio back in; I am NOT advocating this method, but I give mine a good thump and it "clicks" in past the two verical plastic strips on either side. If it's the original Becker, loosen the scew retaining wedges on the radio sides.
The switches are rebuildable with a lot of springs and ball bearings inside (work over a large white towel on a bench or table) and almost always work after being tended to. If you remove the accordian boot at the door to check the wire, the boot will be destroyed on an '81. Check continuity another way.