I read somewhere the hole size needs to less than 1/10 of a wavelength or about 2 milimeters. With such a large dish for Ku you should get some kind of signal although don't be surprized if it performs like a 30" dish. I'm not familiar with your LNB but if the f/d ratio not does not match the dish it will futher limit your performance.
I would give it a try and see what you get thats half the fun of this hobby.