I'm shocked. American Anodizing out of Fort Wayne, Indiana. They've been in business a very long time, have a great reputation. One of the few businesses that do small-batch jobs any more.
They were very apologetic, offered to remove all coatings, and return them free of charge.
I'd never heard of this "die cast doesn't take anodizing" before, and I've done a bunch of reading on it, as I had contemplated doing this myself.
Unsure of what I'm doing next. I didn't like how the gas cap or carb tops turned out with the gold spray paint. Maybe powder coat them all gold? Still undecided.
On to more positive things. I got my filter adapter plate from xs650shop.de and wanted to determine the correct filter for it before I installed it. I don't want to be stuck having to order from Europe every time I need one.
My initial guess was a Smart car. Man, I was right! 2018 Smart Fortwo 1.0 liter naturally aspirated. A Wix 57207, $15 shipped:
IMG_1576 by
michael delage, on Flickr
These were filters that didn't fit well, but would work in a pinch (less than 2 turns engaged on threads, will hang down too low, etc)
IMG_1560 by
michael delage, on Flickr