So yeah, I'm an idiot... I mounted the bars within 1/4" of the stem and they are on just fine now. I'm still not crazy about the plastic shims though as I can see the bars coming loose over time. I guess if that starts happening with any frequency then I'll look into getting some rubber insert to put between the shims and the bar.

Now it looks like I'll need to spend some more time this weekend tweaking the length and rotation of the bars to get the feel just right, but at least I got them on there now which is an important first step, LOL ;-)