RE: 3 blade or 4 blade prop for TF p-51
The problem is:
1) VERY few Mustangs had 3-blade props
2) 4-blade props on models are very inefficient
3) a "Scale" size 4-blade prop would be about 16" but you can only go about 12" on the model (Maybe 13 tops)
So you'll have a prop that has 4 blades, like the real thing, but it will be inefficent and too small to look scale anyway.