2016-12-22 Edit: I've prototyped the design below in plastic with a 3D printer and it needed significant changes. The hole dimensions were perfect, but the dog bone shape needed work to clear parts of the calipers I did not account for. I will post the newer design eventually. If you're going to reproduce these, wait for that post.
I designed replacement caliper adapters that I've been meaning to do for 10 years
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Mine are aluminum and the threads always strip. I'm on my second set of adapters and they stripped a while back. I've spent years and years avoiding removing the bolts due to fear of stripping. Part of my problem is that my adapters are only 9mm thick on the knuckle side (for 3mm more caliper clearance than the normal Fastbrake kits) so I have even less thread than anyone else. The application also calls for red Loctite which makes stripping more likely upon removal. It's really the perfect storm of aluminum threads, not enough depth of threads or engagement, and red loctite.
Not only that, but my second set of adapters weren't actually made right, and they place the caliper just a hair too far out from the rotor so all of the pad material does not contact the rotor. Maybe 1mm or so overhangs the edge of the rotor. =/
I wanted to do steel adapters, but that's too expensive. I wanted to do aluminum with steel threaded inserts but no one seems to make the style of insert I imagined. So I'm taking advantage of flange nuts to act as the thread inserts. Seems like it should work great and be serviceable if threads ever get damaged (which they shouldn't).
Titanium flange nuts are affordable (some motorcycle uses the M10 x 1.25 size I want), so I plan to use them, but stainless steel would be a great option as well.
I'm waiting on the nuts to arrive to finalize the dimensions.
For anyone who wants to do the same, the center-to-center distance for the holes in the steering knuckle is 130mm and the center-to-center distance for the mounting holes in the Wilwood Dynalite caliper is 5.25" (or 133.35mm). The adapter should place these two sets of holes ~33mm apart from each other to work with the VW Corrado brake rotor (or whatever rotor it is that Fastbrakes sourced). The adapter should be 12mm thick, unless you have an odd-ball setup from Fastbrakes like me.
Oh, and the bolts are M10 x 1.25 but you can use M10 with whatever thread pitch you want if you're making your own threaded brackets or supplying your own nuts.