Rich,
What I try to do is to cut down the diameter, but try to maintain the overall original blade shape. This will often get into the "tounge" area of the prop, and may cause some other effects, which may or may not be desirable. After you cut the prop down, you must then thin the leading edge back down to what it originally was, as well.
Clay,
You touched on something that is every bit as important as a well balanced prop, but few actually go to the effort of doing. Even if both blades are the same "length" from the C/L of the hub, non-matched blade shape can cause significant performance loss.
I use what we in the machine trades call "impression wax", which is actually a very low melting temp thermoplastic. It takes some time, but after you get a prop shaft melted into the wax, you can then make an impression of one blade and match the other on to it. This is the first thing I do after making the basic "re-sizing". Then I thin the blades down, hand sand all remaining casting marks out and THEN I balance the prop. I can put as much as ten hours into a single prop, depending on what I want to do to it. This is why I don't do props for other people.
Thanks. Brad.
Titan Racing Components
BlackJack Hydros