I bolted a Firm Feel rear bar in my '70 , but I'm using a '68 B-Body Dana with Dr Diff's inset hanger kit.

There's no reason you can't bolt one in to your car too. The chassis mount brackets slip over the frame and are screwed on to hold. The bar end mounts simply sandwich above the springs and between the rear end housing.

Call Firm Feel and tell them you need a rear bar & installation kit for your wider rear end. The bar ends need to reach to the middle of the leaf spring.

You can see the end links in this photo.