Mystery solved. I spoke to Chris at WCF and it looks like the lower brackets are supposed to be "L" shaped to grab the lip at the lower back side of the bumper. Mine are flat, no bend.
He's going to ship me out the brackets. It's a very clean set up. Allows the aluminum brackets and license plate to "float" so they don't touch any bodywork...
1984 Indy Fiero
[This message has been edited by ag9123 (edited 10-03-2014).]