Try emailing him at dtrlpf@gmail.com. You aren't likely to get an answer to this thread as the last post was almost 16 months ago. Posting to these old threads is necro-posting and is frowned here.
I like the big 20mm chunk of copper, I need to order a 20mm drill and start building for it, I bet it will help transfer heat and reduce heat induced power fade by some amount especially for longer duty cycles.
Also the longer full copper backs with driver pocket are a nice feature.