I believe they are riveted from the inside; you don't have to get them out that way, though. I can see 2 pop-rivet tails in the back of the cans on my '73. I bet if you drill those out, you can take the whole can out of the bezel. Then you can just re-rivet them from the outside.
I don't know if there's any "fix" for the socket in the bad one I have. (reverse light, so I really don't need it). it seems like its rusted in there pretty good.
Andy at Inland RV has the replacement fixtures. I asked my local dealer if they had them..they pulled out the part book, and handed me the wrong part off the shelf. (porch light...same lense; different fixture. the porch light has a chrome flange around it, and won't fit into the tail light bezel). They even went as far as to call JacksonCenter...that's the info they have, too. So I guess Andy is the only person that knows the right part! LOL!