Originally Posted by
ThayerRags
The German Singer 401G and Singer 431G have 3-prong upper receptacles, but no lower 2-prong receptacles. I’m not sure about the 411G and other German 400 models.
411G is the same as you describe as well.
The extension blocks I have - I think I still have 2 are the right angle ones like Manalto shows too. I think I've seen both in the Singer Parts charts though.