The kit from Speedway is a good basic Watt's linkage. If you could mount this off the front of the center section with a rod going to either frame rail it would work excellent. The bars on a Watt's linkage have to be mounted so they are equal length and parallel, then the rear end will remain centered under the car throughout the entire range of motion of the rear suspension. It does get a bit tight with ladder bars, but is by far the best setup.

If you only have room for a Panhard bar you would want it as long as possible. For example a bracket off the center section that is angle to the right as much as you can, then the other end of the bar mounted to the left frame rail making the bar itself as long as possible.

I don't have one mounted right now, but the basic Speedway kit is the same as I pattern mine off of. On lighter cars, I usually make the tubes out of heavy wall aluminum tubing. Much lighter, plenty strong, and they polish up very nice.....