No, butt plate is not curved (from top to bottom). On the width, it tapers slightly on outer edges. Thanks for continued input.

The grip cap is a style that was available to American gunsmiths in the early 20th century. I have had older guns with this type of replacement grip caps.

Then the buttplate is most likely not an actual Trojan plate if it is not curved. This type of buttplate was used on Many different guns. LC Smith, Ithaca, Savage/Stevens, Fox, etc... Not to mention several aftermarket plates too.