I've seen the GMPP heads before & they're nice. For the money there are plenty of better options IMHO, if you want to do cnc stock castings why not do the PRC cnc head exchange program? You send your heads in as cores & get ported ones back for under a grand! If your going to spend big $$ the only way to go would be the PRC 255 or 260 heads IMHO! 380cfm capable out of a head that has better p/v clearance, smaller chambers, virtually stock side runners for better velocity, and they can still use your stock rockers!
Jason