I agree whole heartedly with rmh's statement above. Building light and straight provide for much bigger benefits to flight performance than the airfoil chosen, within reason of course. The laminar flow airfoil of the Mustang is really not that radical and has been used successfully on much smaller models of the P-51 than what you are building. I recently completed the design for a 1/4 scale P-51D which is as scale as my documentation and research would allow, including the airfoil. Best of luck with your big 'stang and please put up a build thread somewhere. Love to see some pics.