Loops for the Rails, yeah!! Had forgotten about those as I have no interest in them. DMS seems to like those 416c style guns. Maybe he can import them for the OP?This was pretty well covered on the 416/417 side. http://www.hkpro.com/forum/hk416-hk417-hq/305322-new-hk-416-lower-partial-upper.html
Determination was the extra holes were for mounting a 416C type buttstock.