This paper reports the application of synchrotron white beam X-ray topography to the identification and mapping of the polytype distribution in nominally 3C heteroepitaxial films grown on 4H-SiC mesas which, prior to epilayer growth, were subjected to the recently reported procedure for producing atomic flatness [I]. Results from studies carried out on two wafers are presented. The first (wafer 1), a non-optimal region of one of the 4H-SiC wafers that was described in [1], was subjected to the procedure for production of atomic flatness. The region of interest, experienced imperfect control of the local supersaturation and significant 2D terrace nucleation of the two variants of 3C polytype was inadvertently produced. This sample served to demonstrate the capability for polytype mapping. The second (wafer 2) consisted of a 4H wafer where more controlled heteroepitaxy was carried out following the successful production of the atomically flat mesas. This sample served to demonstrate proof of concept, i.e. to confirm that dislocation-free mesas could be made atomically flat and that complete DPB-free coverage of these atomically flat mesas by one or other of the 3C polytype variants could be achieved. For both crystals, back reflection topographs revealed strain contrast bounding regions that had experienced 3C growth. The apparent mismatch between substrate and epilayer was further investigated using High Resolution Triple-Axis X-ray Diffraction (HRTXD). Preliminary Deltaa/a and Deltac/c values obtained for the epilayers are presented.