The XFM-1 had turbocharges on the outside of the nacelles. When modified into the YFM-1, all the literature I've seen say the turbochargers were moved to a position "in the bottom of the nacelles". The 'Operating Instructions' for the YFM-1A even say the turbocharger is "installed in the lower surface of the wing under each nacelle."
But I've never seen any illustrations or pictures of such an installation, and I'm not sure it's even possible given the configuration of the nacelles and the full span flaps on the airplane, so........... anybody know anything about this?