I'll correct one thing: Panhard rods are NOT just for circle track cars. They have been and still are production items on some RWD vehicles, and were used successfully on most or all of the successful RWD rally cars in the 70's and 80's. My 70's vintage Opels all came with them from the factory and had a very good rear live axle suspensions, as well as my 2016 RAM pickup (where a panhard rod comes with certain options).
Yes, use the rubber bushings for sure; it will avoid breaking stuff if you kiss a curb. The chassis mount has to be good and strong.
MOST importantly! Study up on how to locate the end points of a panhard rod. THAT sets the rear roll center height above ground for a live rear axle. You can make the locating points variable (typically by using a series of vertical holes in the chassis end connection) and use that to adjust the rear roll center height. You can use that to tune in the F/R cornering bias (just like they do with an adjustable track bar). It will also be useful to have the chassis end connection point adjustable so that you can change rear spring height and then independently set rear roll center height.
Note that it is normal to have the rear roll height a bit above the front roll center height, but not TOO much higher, so some work at figuring out the front roll center height is in order. A and B body stock front roll centers are often at, or even a bit BELOW, the road surface, so if you don't pay attention to the rear roll center height and get it high, the rear is going to want to wag and roll the car all over the place. I have some calculations somewhere.....lemme know if you want further info. (It's not exactly rocket science to figure out.)
I would be looking at using a tubing diameter in the 1" to 1-1/4" range.
