If I still had my old scrap discs, I'd have sent one up to you for a test fit.
You're definitely going down the R32 route, so could be an idea to buy your 345mm discs and test fit the setup on one side before you start painting and buying brake lines etc...
Given the uncertainty, I'd call Darkside tomorrow morning. As you've pointed out, they have definitely made these calipers and a 345mm disc fit a mk5.