I have a Gottlieb's Count-Down where I have taken everything off the playfield (for when the repro playfield comes out), and another one that I am using until then. I had thought that all pop bumper rings of that era were the same, and I have a few that I have inventoried over the years from parts machines tear downs - but it appears that the Gottlieb's part is 3-13/32" long while the others are 3-1/4" long. Is the Gottlien one part # GTB-A16634, while the others are WLL-A4754, or perhaps A1873 or A967-00013-000?
The Pinball Resource seems to be out of stock for the 16634+, and the stock ring has a bit more corrosion damage than I would like.