Okay...I changed to a different icon theme, so the desktop used the default KDE "K" icon for the menu.
I logged out, and logged back in as root. I went to /usr/share/icons/default.kde/48X48/apps
I selected/cut "kmenu.png" and pasted it in an arbitrary folder. (Temp)
Then I got my custom icon, made sure it was named "kmenu.png", and pasted it back into the original apps folder.
...logged back in as user, and there it was...
...probably pretty simple for most of you, but it's a small victory for me.