Tip: If you have an Image-Processing program such as PaintShopPro you may find it informative to grab a copy of these photographs and play around with the image contrast controls and any false-colour filters you may have (such as the PSP "Solarize" option). Even a moderate amount of contrast will help to enhance the crop-marks.
raw 250dpi scan with no image-enhancement
Most of the old Abbey Fields site can be seen in this close-up view from the top left corner of the postcard. Cropmarks are visible in the field which tantalizingly hint at subsurface features, most of which are probably attributable to the old Abbey itself, but include what appears to be the south-east angle of a Roman auxiliary fort.