I bet it will make beer, which is always my primary goal. Sometimes experimentation results in a better outcome than trying to follow each detail in a recipe. I always believe I will screw something else up, so trying to replicate someone else's beer is not a huge concern. So many things can be different, water chemistry, boil time, crush, AA of hops and many more. I would say mixing C20 and C60 will not give you C40, but it will make beer, and it may be better (to you) than the C40 alone. I say go for it.