RE: Prop choices for .020, .049 and .061
Since your scratch building, the prop your looking for is likely to be found by you. A good starting point is to use the largest prop in the manufacturors recommended range. Reducing the pitch will allow the larger props to give more rpm and allow the use of larger diameter more effiecent props. The norvel engines need to turn some rpm's to make power. I hope this helps.
An example for a .46- (not accurate---exaggerated for clarity)
10x7 - 16000rpm fast prop (100mph) 6lbs thrust
12x4 - 16000rpm slow and powerful prop (60mph) 12lbs thrust