Hey Jason,
Like everything, there is no "right" answer, it all depends upon what you are looking to get out of the car. As for the length of the links, longer is better in the general case, the suspension will handle transitions more smoothly (things like the instant center, virtual swing arm length, etc transition nicely relative to a setup with short arms). The ratio of the upper to lower will mostly manifest itself in pinion angle changes, and here again, there is no "right" answer, but I can offer this observation. Usually, the folks that supply three links are trying to fit everything beneath the factory sheet metal, and as a result, the upper link tends to be really short, like the new Mustang's. This is FAR from optimal, and not only do you get pretty dramatic pinion angle changes, but the rest of the important suspension characteristics change really rapidly when the suspension compresses, droops, or rolls. The result is instability, which can sometimes be tuned out with shocks and springs, but usually not, and certainly not for a car that will see a variety of road conditions. Honestly, this is a case where "size matters," and anyone telling you differently is trying to sell you a packaging compromised setup. It is a really easy thing to show on paper, and a really easy thing to show in reality too.
A decent place to start is to make the upper link about 70% or so of the lower link length, and I stress, this is a "START," not the end-all answer.
A really long Panhard Bar is a great setup, they can work very well when executed properly. In our setups, we use the Watt's, with the bellcrank mounted on the frame. This solves two issues, one, it eliminates lateral axle motion in bump/droop/roll that is present with the PHB, and two, it fixes the "roll moment" of the suspension system, so the springs and sway bar see a constant roll force, independent of the position of the suspension bump, etc. It's more complex, but in our opinion, it's worth every last cent.
Best of luck with the project, sounds like a bunch of fun!
Mark
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