Hello friends, I have found a high resolution image of the 1928 Oshigata of Honjō Masamune published in Tsuguhira Oshigata. Per Mr. Guido Schiller, it seems that this is the least detailed Oshigata, but it seems to be the one most commonly used for demonstration. Here is the file uploaded to Wikimedia Commons: File:Oshigata of Honjo Masamune (1928).jpg. I have also attached it to this post.