mild street suspension question

Rear bar will definitely reduce understeer (plow). Rear spring spacing between the F/M/J is not the same as the A-body. Ends of the rear bar won't line up with the A-body without some torch time. The A39 Dart cop car ('76 option, I think) had a rear bar, most delivered in SoCal. The bar was body mounted. I'd like to find part numbers for the spring plates for mounting a bar on my car.