Can't decide on heads. . opinions??

What is the purpose of your build? Race car? Street? Street/Strip? 270cfm head flow can support at least 500hp. You would have to have quite a bit of compression & camshaft to make that with 340 or 360 cubic inches. If you want some serious flow, but stock valvetrain, intake, headers, etc. Look into the Dr. J's Airwolf heads.