While the previous replies are totally correct - there's an even simpler solution once you realize the 670 is just another rifle like hundreds of others different makes, and that ALL of them use similar sights.
It's just that sometimes minor sight details are different from rifle to rifle, like the height or base width.
SO, while a replacement Winchester front sight is certainly OK, ANY other front sight blade (Williams/Marbles/Lyman/etc) of the proper height will also do just fine - especially on an economy rifle like a 670, where many owners choose to upgrade the type of sight from issue to (say) a gold bead, ivory bead, or fiber-optic.
That's why wholesale suppliers, like Midway/Brownells/Williams/Marbles/Lyman/etc list the sights by size, rather than application - AND you couldn't find a reference for a specific rifle.
The only sights that are usually listed by application are those that mount in a position that has a contour that may vary widely from rifle to rifle - like a receiver peep sight.
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