Go with a Pahhard bar. Watts links are neat, but if your car doesn't have much wheel travel, they are a waste of time, effort and weight. Just make sure you have the track bar fairly level with the ground at ride height and right on your desired roll center. You could try brackets with adjustment holes so you could find out the right rc position for your car.
Go with steel tubing with threaded spuds in the ends to accept spherical rod ends. Or, just use a heavier-wall tube and thread it. Axle and frame bracketry will be the biggest fabrication challenge. I imagine you can find brackets from a stock-car catalog, then cut and fit as desired.
By the way, what are you using to locate the rear axle now? Assuming it's a bouncing axle, have you considered an IRS?