No, definately not Portuguese, though I can see why you think so. There is a *very slight* resemblance to the Portuguese M40. Very slight! See the real thing here - .: World War Helmets - Casque Modèle 940 :.
What you have is actually Spanish, a M34 (also known as the Eibar, from the name of the Spanish munitions concern that designed and made it). In service from the late 1930s until really much later, maybe the 1970s! Examples would have been repainted and refurbished many times. As yours has the litle badge-mounting clip on the front it dates from after the end of the Civil War, as the badges were a Francoist institution.
Awesome! Thanks Greg