Sorry, I'm a bit late reading this.
The USM8 short frog was early, then there was a modified short frog with a hanger, and then the later long frog modified with the hanger. The M8A1 came later.
I pulled some out a took pictures.
Jim
https://www.milsurps.com/images/impo...erentM8s-1.jpg
https://www.milsurps.com/images/impo...rentM8s2-1.jpg