What Mame button is what MK button has been changed a few times in the Mame code, I think...
If you want to know, just fire up MK, push Mame button 1, and see what the guy does. You can usually distinguish between HP and LP etc. pretty easily.
And you need the Run button for lots of the fatalities and combos and stuff, so it's best to have it accessible. I put it as the middle top button on my setup, cuz I don't have an extra button-4.