Why didn't you go with this Eibach adjustable link?
https://eibach.com/us/i-12083-eibach...255-285mm.html
This seems to be the adjustment you need, and its a 12mm bolt. They have them in stock for $100 for the pair. I have been considering the same thing, and I might do this now. For the rear, I bet you can buy one link of each size, then swap ends.