ASM has a bad rep....
But, my limited observation is that at the time they were being manufactured that were ahead of most of their competition.
I have frequently found it hard to find the markings on ASP pistols. When the OP said the pistol was un-named, I thought perhaps it was ASP because of that similarity, but I (just as you said) don't think ASP ever made a Walker.
Palmetto would have been clearly marked and I think Uberti would too.