My matrix is an armalite pattern upper with DPMS pattern guts. I've seen threads where people posted pics of guns using mixed barrel/bolt setups that headspaced and ran just fine. I've seen posts of people with both platforms who micd them out and found no appreciable difference, and others who swear the lugs are longer, or the face is deeper, or the lug spacing is different, or they know a guy who knows a guy at armalite.
If at all possible I'll try and keep my parts the same because I know it works. If I find myself in a position to have a mixed setup, I'll headspace it and then go shoot it. I'm willing to bet the difference between AR10 and LR308 bolts is no worse than the tolerance stacking you end up with mixing manufacturers of LR stuff.