I think the ones in my 1973 wagon kick panels are molded from  some sort of abs or polyethelyne. It does melt and can be welded with a soldering iron..  but only for cosmetic appearance.

I repaired a couple of cracks in my kick panels where they cracked at the top where the kick panel bends around the door frame.

I wasnt able fuse the crack together on both sides (front and back) but wasnt able to get enough penetration to keep the crack from reopening.

The previous owner had tried to patch them with bondo on the backside but it didnt adhere.. so you probably wont be able to glue them.

Mine were cracked at the top where they bent around the door frame.  i drilled some small .030 holes on either side of the crack and used some 18 gauge wire as a "staple" to hold the joint together.

You might also try making a backing plate from thin aluminum sheet on the back side to cover the area on both sides of the crack and pop rivet it on both sides of the crack for structural integrity then fusing the edges of the crack together with a soldering iron for cosmetics.

Or you might be able to glue on a backing panel with contact cement, then fuse the crack on the front side for cosmetics.

The rear panels in my wagon seem to be made of a different material..much less flexible and somewhat brittle. Mine tend to scratch easily, but I haven't had to repair any cracks . Just paint over the scratches.

I dont have a radio bezel but I do have the heater control bezel and I think it is either styrene or abs and I think the radio bezel would probably be the same and I would suggest trying super glue if you are able to get a seal between the sides of the crack.

Get some aluminum window screen and use a soldering iron to melt the screen into the plastic over the crack (back side obviously). This will reinforce the repair and it will not open up again.