You can make a very good pitch gauge for not too much cash with a protractor. The Prather gauge was not all that accurate, as you could skew the measurements by a number of ways.
To build a prop gauge, I would start with a good digital protractor like this General Tool model for $30.
Next you need a measurement board. Use a flat sheet of aluminum, about 1/4" thick or maybe slightly thicker plastic that is a bit longer than the largest prop you want to measure and maybe 4 to 6 inches wide (It will need to be pretty wide to measure flatter angles at the tips of props).
Drill and tap on one end for the different stud sizes of the props you want to use. Might be three or more sizes, but if you run out of room on one end you can also use the other end too.
Finally mill or cut slots through the board for the protractor arm to go through the base at the spacing you want to measure. As I said before, the Prather unit's station spacing was in cm, so if you want a direct comparison to a Prather, go with that.
To use, mount the prop using a short thread or bolt to the base. Insert protractor from the other side and take a measurement. Do the math to find out the inches of pitch at that station.
If you find out that one blade is higher or lower than the other, don't change the blade, change the hub. If the front and the back of the prop hub is not exactly parallel, then it's a good chance that blades won't track in pitch. You can scrap the rear of the hub with a single edge razor blade to get them right with each other. Then go ahead to change each blade as desired.