Ricky, I am a clone builder. We work with "real" Mk12s, and also .308 variety, like Mk11 and M110.
If you have not done it before, a do it yourselfer for .308 is hard. I like analogies, so bear with me. Spanish is Spanish for those of us who know how to ask for "dos cervesas par favor," and that is the extent of our linguistic skils. But, my mother grew-up in Puerto Rico, and she had trouble speaking in Madrid, and does not understand Mexican Spanish. Then there are the Catlonians in Spain, who really speak another language. Forget about Portuguese, for which most of us think those two countries should be able to understand each other.
Not much is standard in the .308 world. Now, an entirely different question is why would anyone want to shoot Malyasian ammo, but I am sure there is a story there...
My recommendation is to start with a solid .308AR full gun from Stag, Armalite or CMMG. They make solid equipment. Then, you can start to customize. Another alternative, if you like the Mk12 SPR type, is to get someone to build you a Mk11 type rifle with a Mega Matten receiver set. Mega is solid, and tends to fit the higher-end rifles, like KAC, LMT and LaRue.
Until you want shoot Federal or Black Hills 168 or 175 grain ammo, I would not be picky on the barrel. Chrome-lined is preferred with ball ammo.
