.070, H2 buffer, Tubbs flat wire spring.
or
.070, H buffer, Tubbs spring, adjustable gas key BCG
or
.070, carbine or H buffer, Tubbs spring, adjustable gas block
.070 is a little bigger than what it should be, but with such a short dwell time on a 10.5" barrel it needs more punch up front to make it consistently work with anemic ammo (PMC 223) all the way to 5.56 ammo. Every time I see someone go too small on the gas port on a 10.3/10.5", it becomes a short stroke nightmare. LMT's are notorious for this. Have them stay in this size range initially. If needed, it can always have the A-fram removed and the port honed out a tad more to get the timing right. Can't put metal back in that gas port though.