The Model 19 is the Combat Magnun, and the Distinguished Combat Magnum is what they called the new L frame models (adjustable sight).
Here's the names off of the S&W Product Guides/parts list of the era:
Model 581/681 - Distinguished .357 Service Magnum Revolver
Model 586/686 - Distinguished .357 Combat Magnum Revolver
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.............SmithNut
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