Hi Howard,
some additions, as promised!
The above mentioned "春田" (Haruta) are, besides the "岩井" (Iwai), one of the oldest schools of armorers in Japan and the region around Nara/Kyoto is, since centuries, known as an center of armor production ("鎧造の里",yoroi tsukuri no sato). A lot of workshops were based there, as also merchants "具足家" (Gusokuya), who assembled every part of armor according to customer reqirements.
For the latter, the Iwai became famous, by the way!
Well, back to your mask. It's a "目の下頬" (me-no-shita-bô, a mask, covering the face from under the eyes to the chin and featuring a nose). A bit complex, I admit....
You will find a lot of masks like yours with an always similar basic shape, but in terms of color, mustache, throat guard, ears, teeths....etc., slightly diffrent executed. So it represents one, of at least two, type of men-pô, those were "mass produced" (I don't like the term) by unknown specialised artisians. Afterwards customized and incorporated in an armor, or perhaps sold as is. The fact, that non of the specimens I came across were signed, should support this theorie?! That said, doesn't mean bad quality at all!!!
Hope it sparks some interest...