I measured the bob-tach for my bucket and it is 44 9/16” ID also. Some of the older Bobcats and smaller models use a smaller bob-tach plate. I know because I cannot use my father-in-laws Rooter for his 610. There are universal attachments that are wider, but they have the locator holes for the bottom pins at different spacings. I found a universal mounting plate diagram from Bradco that is 49.5” wide, note the four holes at the bottom for different machines. See the diagram at http://www.attachment.com/pdf/specsheets/Adapter%20Plates.pdf
I don't know how wide the mounting hardware is for other skidsteers, ie.: John Deere, Case, Cat, etc... If you find out please let me know because I am looking at building some of my own mounting plates also. Hope this helps.