Hi Jon,
menpō can be divided in several types with quality ranging from average to piece of art. Unfortunately not much is written on the subject, even though they represent an interesting collecting field in their own right.
However, back to your piece. Hmm, how should I put it….well, it looks very odd! The mask pretends to be a ryūbu-men (mask with calm expression, usually without wrinkles). Actually, some features in the design and workmanship are raising doubts that we are dealing with a real menpō in this case. That is also true for the throat guard (called “tare”). Nodowa is a different piece of armor!
We can go through step by step if you like, later on?!