Oftentimes, the numbers we find cast into parts is just a "casting number". There are some cases where the casting number is the same as the part number, such is the case for the FD11…But, when you look up the part number for the 1958 model with the stop switch, you find a completely different part number than 580210, even though your later model mag plate has this number stamped into it.
In both cases, the same basic "casting" is used, but there is an extra hole added for the 1958 models with the stop switch, which is why it has a different part number….
Oftentimes, the casting numbers we find on parts do not correlate with the part numbers in the parts book….