I have a complete lower I want to top off with a varmit upper but really have not seen any except at the SHOT show in Jan. I want to keep the gun 100% RRA so would like some feedback as to any specific style and also barrel lenght, etc. There is a long wait on these so I want to get it right the first time. Also what about a reasonable scope? I have purchased some from CDNN but will probably like something a little better without breaking the back.