LA cyl head challenge !!

Just scheming for new build next year and trying to prepare can use iron or alum but want the highest flowing LA cyl head NOT USING OFFSET ROCKERS and engine will be 340 inches single 4 barrel roller motor with lots of compression 1/8 mile manual trans not street motor thanks .
Dave @ KG Engines in OH claims he can CNC factory X heads and get 280 cfm @ .650 lift for $750
I have checked him out with a couple of sources and they all said he does very nice work.
I am thinking of have my X heads done this fall when I remove them to swap out my jagged up hyd roller lifters.