Well, the "unit tests" that I wrote about in the last post only take you so far. When I went to mount the parts I realized that I hadn't made recesses to accommodate the rivnuts that I had inserted into the radiator. Rivnuts (aka rivet nuts) are really useful and if you don't know what one is, this video does a pretty good job explaining it.
In the picture below, you can see that have been installed in the radiator (silver) and that they have a lip that protrudes. A simple thing to fix, but it required me to print the parts again. There is an unused rivnut sitting on top of the condenser (black). Rather than using wimpy aluminum rivnuts I opted for zinc-plated steel ones. In addition they're ribbed for the the condenser's pleasure... ahhh, I mean to help prevent it from spinning in the hole.
The unit tests aren't a guarantee, but they a did allow me to quickly refine the design. In any event, I'm really pleased with how the brackets came out.