The best for you John is to pull the rod while attached to a scale until you feel it is bending to where it should be at maximum. Then check the weight you pulling on the scale. If the load is 10kg X 3=30kg=60Lb it should be a 50Lb rod. You can also compare it to a similar known rod. Another option will be to check the net for similar blanks and compare the dimensions. The tip diameter will give you an idea. If you are going to rebuild them, make notes of where the guides are placed before you strip it. Copy what's already there.