The I-beam is just a plastic "girder" you can get at most hobby stores. I just cut it to a reasonable length, removed the spring from a stock I-beam and slid and glued it into place on the girder. There are no tracking force gradations on the girder, but I didn't use those anyway. -I just set the weights to obtain my prescribed tracking force and wiggle from there by the sound.
As to how far out to go, use the least weight possible for your cartridge, and move out until the base response starts to deteriorate. This might change with adding a spring or two to the I-beam. For instance, I started with just the weight that the other weights attach to and had that way out the beam. -No go. Had to add a weight and go from there further in on the beam. -Complicated, eh?
Today, I received springs and I-beams from Bruce, but I think I'll stick with the long I-beam, and add a spring or two. -Sounds like two springs will work for my low compliance cartridge, but experimenting is half the fun.
I use the term antique for my system because the amps, speakers, turntable, and arm are all 20 years old. They work well if you know how to maintain them. I've
learned over the years to do all my own maintenance and mods. It's amazing what you can do with a soldering iron, voltmeter, and decibel meter (Radio shack and vintage).
Thanks for looking at my humble system,
John