Clifton Laboratories was acquired by DX Engineering. The Clifton Laboratories website is now redirecting to DX Engineering, and the Clifton Lab references and papers are unavailable.
The original K3 AGC paper from 2009 is available on the Internet Archive’s link, or here. Recent Elecraft firmware upgrades have expanded some of the ranges of the parameters, so certain aspects of the paper are no longer accurate. Fred, KE7X, author of guides particular to the Elecraft models, discusses the most recent AGC related firmware changes on his website.