Your issue is gonna be the bolt. 6BR uses a 308 (.473") case head, which I'm not sure you can even fit on an ar15 sized bolt, or if you can there will be very little material left on the bolt face after you cut it to fit that case head. If you jump to an ar10 platform, you are gonna run into feeding issues with the short cartridge, would have to build a spacer system into the magazine I would imagine, like how MDT does with their 6BR AICS mags.
For AR15 you will need something based off the grendel case/case head of .441" or the 6.8 spc case/case head of .421". so 6mm ARC would be the easy button, as there barrels, mags, bolts, head stamped brass, dies, factory ammo, etc for. Or a 6mm variant of another ar15 cartridge.
For AR10, 6mm creed would be the easy button. but there are lots of options you could go.