Progress has been made!
Last January when the ke arms kp15 lowers were announced, I preordered 2 stripped. I got my hands on a low serial numbered black one on Christmas. I promptly started dremeling and drilling and tapping holes. I am very impressed with it. Nay say all you want, but until you have one in hand, I will disregard all criticism regarding the lowers. This is a superior product in my opinion.
Anyways, I have come up with a plan for the upper. I still do not know if it will cycle reliably with a carbine buffer. If not, I will build a rifle lower.
I ended up ordering the brownells 605 barrel and slim Faxon muzzle brake. I have the aero altas one 12 inch mlok hand guard that I intend to use, it comes up directly behind the rifle length sight post. I am still trying to find a black slick side carry handle upper.
Both ke arm lowers will be pretty much the same, I ordered both colors. I have most parts to finish the second one, but not everything yet.
I used ke arms slt2 trigger with their 45 degree ambi safety (can put on safe when hammer is up), aero pdq lever (ambi bolt release), Norgon ambi mag release, jp enterprise buffer, and grov tec threaded sling mounts.
I had to dremel on it some for the pdq lever, I drilled the hole for the safety detent all the way through and tapped it from the bottom to hold the spring, and tapped the holes for the sling mounts. I only used 3 springs, 1 plunger, and 1 trigger pin from a standard parts kit. I may change out the fancy pants mag release button for a regular mil spec one (not the ambi mag release). I did not put in the buffer retainer parts because I used the captured setup.
I do not trust the bathroom scale that I used to weigh it, but it claimed 4.6 pounds. I was expecting 5.5ish. The upper currently on it is aero slick side upper, Faxon midlength 14.5 pencil barrel with pinned and welded flash hider, geissele ambi charging handle, aero atlas one hand guard (I intend to switch this to carbon fiber and use it on the 605 upper), and sig Romeo 5. It feels very much like a toy.