It's been a while, but I have used Alaskan Copper for some larger specialty flanges in the past. As I remember, they have some of their own designs which are not exactly standard.
...there are no standards that govern 26"+ slip on flange dimensions.
I had already found dimensions based on industry practice in Trouvay & Cauvin Piping Equipment 2001... but our 36" slip on flanges have a smaller hub length than listed.
My next question is: What is the procedure for repairing slip on flanges? Would it result in funky hub lengths?