I' have an old proof printing frame that I use to apply pressure to the negs filed in print file, held in contact with the paper to be exposed. I have adapted the frame over the years to include a black foam core insert the size of 8x10 paper that allows the paper to be aligned in the dark. I align the paper by feel against being square to the edge of the print file papge, and then put both of them, while held together into the frame and align it against the edge of the foam core. There are occassional slight mis alognment,s but none that make the contacvt sheet unusable for my reference purposes.