if i were you, i would put the car up on jackstands at the frame in the rear and use a jack to drop the axle down and see if i could compare the arch of the original springs and the XHD springs.

the XHD springs are supposed to be just like the factory 440/hemi springs, and there is an all original Coronet RT i've seen a few times and that car sits pretty much perfectly level at a moderate ride height.