I have a 100 year old beautifully made 9 foot octogonal 3-piece fly rod with a wood (swollen style) grip. Actually it may be called a 4-piece as the grip accepts the male end of the rod as well. There are 10 furrels. I cannot determine the correct floating fly line weight to use. There is no visible indication on the rod itself. How do I determine the correct line weight?? Thanks in advance. Excellent forum!