Yes, the gringo-mexican war idea fits perfectly.
But I thought the love story. Does not fit in my opinion.
Here simply lack the coolness that simply belongs to a Spaghetti Western.
If I want to watch a love story, then look no spaghetti western.
And when I watch a spaghetti western, then I will not see any love story.
Leone, for example, never had a love story in his films.
On the contrary. In For A Few Dollars More, there was a bed story between Eastwood and the wife of the hotel owner. But they are not used by Leone. He feared it could undermine the coolness shown by Eastwood.