I did the same thing a while back but used the GTO smoked tail light covers and painted the insides black. I actually used the exact same hole configuration as yours
I scrapped the idea though when I mis-aligned one of the holes too close to the one above it...
You can also use 3M Dual-Lock fasteners (Target...$5)... rock solid
I'm glad yours is working out!

Good luck and let us see pics at the end!