Thank you for the clarification--seems like it should be straightforward enough. I was worried I would have to drill out and use rivets.
Incidentally, what may have caused one of the two little "tabs" as you call them to have broken off, and how does the absence of that small bit of plastic cause the roller to fuse against the rivet above it when it passes one specific section of track? I realized I do have one other old caboose in the closet that has a light in it, and I ran that one last night to see what would happen. It lit up fine with no issues after @25 passes around the oval loop, and this would demonstrate that the tab piece breaking on the 6557 plate assembly wasn't caused by the track.
Also, I was curiously surprised at the few number of options I found on the internet to buy a 481-10 base plate, as opposed to the more readily-available 481-10t. I decided I like the coupler without the tab better--none of my other trains have them--and so I went with a 481-10.
