FWIW - A picture of three bases L-R: model 1902 rifle, model 1898 rifle, and model 1902 carbine. (I didn't have a model 1898 carbine base to put in the picture).

The second picture is an unofficial sight, (I made), using an 1898 base and 1902 top. It is on a cut-down Krag.
Joe DeChristopher made such utility sights for years using surplus parts: he clearly sold them as such.

BTW - Lots of legitimate model 1902 Krag sights were repaired using a peculiar slotted  'locking-screw knob' originally made for the 'Rod-Bayonet' 1903 Springfield.

There is a lot of interchangeability of parts between model 1898, 1902, and early 1903 sights

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