My lens is the 250mm SF , that lens uses a Copal 3s shutter rather than the Copal 1 shutter on yours .
Theses a big size difference between the two , the the measurements of mine won't help you .
You could possibly scale down , in which case , check out #8 on this thread ;
Are the soft focus disk for the 180mms and 250mm lenses the same size/interchangeable?
When you unscrew the front of the lens , the SF disc just clips on , so you can get that measurement of your lens .