Loopman,
I have the same spinner. I made a template out of paper for the prop openings for a precision fit and so that they were both the same. Then I used a 4-40 tap and button head screws. Be very careful tapping aluminum! Use lots of oil and go slowly to prevent your tap from breaking. The Graupner 15-8 x 3 blade prop would work best for a Saito 180. These are great props. I have used them for many years.
Dave