They’re nearly the same machine, but there are some differences. Few of the model 27s were intended for electrical use, while most of the model 127s were. That’s the major reason for the high and low bobbin winder difference, but Singer continued manufacturing both models at the same time for a number of years. Not all countries, or even parts of countries were getting electrified at the same time. It took years. Singers BWs were high on 127, low on 27, but electrification changed that on a lot of 27s. All it took was to make a belt guard with an arm on it, and move the existing low bobbin winder up onto the arm and add a rubber ring (tire). Originally, most Singer 27 bobbin winders were powered by the treadle belt down at the low position.
Another major difference between the 27 and 127 is the balance wheel design (6-spoke & 9-spoke). They have different length hubs and different height shoulders.
As to your converted machine, we’ve got to remember that the coming of electricity meant that most sewing machine users definitely wanted to convert to electricity. Some were afraid of electricity and didn’t convert, but the majority of treadle users did. That’s why your model 27 looks so much like a model 127. That’s what people wanted it to look like. Those solid disc wheels completed the “look” for one thing, but they also made the bobbin winder work in the high position (taller shoulder). Companies (other than Singer) started making the solid disc balance wheels, and they were available to independent shops to rebuild the then unwanted, non-electric 27s. The solid disc wheels were even available for the long hub machines in two models (#1241 & #1243, both wholesaling for $2 each in 1951). One (#1243) featured a “large pulley to slow speed”.
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