Ed,

I had the same engine in the same aircraft. Great combination. I ran mine with an 18x10 or 18x6-10 with great results. The suggested 20x8 should work as well.

If you will send me a PM with your email address, I will send you a copy of the manual. Ok, it is for the Quadra 42, but they are the same. I have both engines.

Have fun with it!

Bedford