I took more pictures. I have one end loading machine like yours - and three other front loaders. I have another White end loader that is older, and it's the same retainer as the Singer 15 above.
These four all have the rotating side clips and retainer ring
This is the End Loader (SBF)
the Dressmaker had the same shuttle as the end loaded (SBF) and the Morse and White each had one a bit different. However the differences were minimal, the were stamped JG2 (for the two similar) and JG1 for the Morse and JG4 for the White.
The retainers were all the same on the flat side - but with this difference between the front loading (left) and end loading (right). I think either would work for the end loader, but only the wider slot one would work for the front loader.
