As for bolt length...I am having trouble visualizing what you are describing. I am using a Sen. Fixed Pitch metal prop and the Sen. spinner option + Van's prop spacer. When I put a prop bolt through all of that hardware, the exposed bolt threads are long enough to completely engage the the prop flange threaded insert.
Actually I was talking about the length of the bushing the bolt threads into and the length of the bushing and the amount the bushing goes into the prop hub. My prop bushing only goes into the prop hub about 1/8" and the prop hub could take another 1/4".
It may be different with a fixed pitch prop since I have a constant speed prop.