Kevin,
We used the same method you described. I can't remember the exact distance we went inboard from the tip, but we used a level in a horizontal position to get the blade level, then used a level in the vertical position to find the vertical level spot working inboard from the tip. We marked this spot vertically on the back side (plane side) of each blade, then measured the distance on each blade from tip to the mark to verify each mark was the same distance from each tip. Then we used that mark to set the degree of pitch with the Warp gauge.

Finally, we set up a gauge on the floor from one blade tip (with the blade tip in the straight down position). The gauge gave a visible location of both the blade length and tip location. Leaving the gauge in place, we turned the prop so each blade was lined up with the gauge, one at a time. This verified each blade was the same length and was set on the exact same track.

One last thing. We did find that the prop was way out of balance and we did have to balance it.