Ken:
Your blade reminds me of another Spanish colonial sword that I posted several years ago here
http://www.vikingsword.com/vb/showthread.php?t=2068 and before that here:
http://www.vikingsword.com/ubb/Forum1/HTML/001235.html.
That sword had a typical Spanish D-guard with a tang peened over the end of the guard. It's Spanish origin was confirmed by an inscription,
Recuerdo Republicano, at forte. The blade of that sword was also flat on one side and peaked on the other to create a triangular cross sectional profile. I think we concluded that it was probably from the Philippines, but perhaps Mexico or elsewhere in the former Spanish colonies where independence from Spain had been sought.
Why a Spanish colonial sword would end up in the wall of an old Irish house is an intriguing question. One could probably write an interesting novel about that! I'm a fan of historical fiction.
Ian.