Thanks so much! Sounds like a good winter project for me. Will get in touch with you 
I can hook you up with a guy that will build you a 300BLK barrel and I can help you set it up. It requires you to cut an op rod down to carbine length though so you'd need to order one of those if you wanted to keep the 223 conversion functional. Buying the rest of the gas system and the barrel nut and handle makes things much easier as well if you plan to swap back and forth regularly.
Once I do some function testing with the 6.8 conversion I may sell the barrel and bolt. Won't be cheap though as I would sell it as a package with barrel, bolt, and mags. It uses standard mid length gas system though so no ordering parts![]()