This was a tremendous help.
I do not have any really short rods. They are all between 8 feet and 9.5 feet. I have one Abbie and Imbry that I put a 3 wt Cortland Sylk on just recently (based on your review of said line a month or so ago) and find that it casts quite nicely. Based on your suggestions, I may measure out 35 feet or so of this 3 wt line and see how it loads the rod.
The other rods are likely to be 5 wts to 8 wts based on your descriptions. One of the longest rods appears quite heavy and I have fished it very briefly with an 8 wt line on it. As I recall, I was struck by the slow action but that may be simply because I was used to only graphite rods at the time and not because the rod was overloaded.
One rod I am most interested to try is a Goodwin Granger Denver Special (8'). It has the original markings on it and the tube but appears to have a weight in ounces rather than a line marking like HDG. My plan is to start with a 3 wt and move up to 4 and perhaps 5 wt line until the loading looks correct. I will do the "parabola test" you suggested before I do anything else.
Thanks again for your help with this.