I have a 73 E body with air and will be redoing some of my rear suspension this winter to get a better ride and handle better. The front comes later. The rough ride is the bigger issue. I remember reading here that the rear spring shackles should be vertical for proper operation and the best ride quality. I see that mine are slanted about 1" toward the rear valance, not vertical. The springs are ESPO's, standard (close to OEM) non-heavy duty, about 3 years old. They have less than 5K miles on them. Never noticed this before. Could they be the wrong springs, maybe too long? What is the best fix to get them vertical as I understand they should be? Lastly, is the ride dramatically and negatively affected by them being slanted rearward? Looking for help and recommendations.

Actually, your hangers are in the correct position. They should not be vertical but should point back towards the valance. The location of these would not dramatically alter the ride or handling. They will create/subtract wedge to the chassis as they move to/from vertical, which isn't great, but isn't a huge issue.

If you feel the ride is harsh, then you need to better control the motion as a standard spring should be reasonably soft.

If you want to improve the handling, most the work will need to be done up front, not in the back. What/Where exactly are you starting from? Sometimes something as simple as the alignment can make a big difference in feel.

From the mopar chassis manual...

Thanks for the feedback. I appreciate the comments and attached picture. Clarifies the issue. I also forget to mention that I have 295/50 15 tires on 8" Billet Specialty wheels and subframe connectors. More on what I have: Monroe shocks (probably too harsh, they are heavy duty), urethane bushings in the springs and an OEM sway bar with original bushings purchased at Nats swap meet. Since the hanger position is not the problem, other plans are to rebush the OEM bar with urethane bushings, put rubber bushings in the front spring eyes and go with Bilstein shocks purchased from Summit. I will measure ride height to be sure to get correct shock for adequate shock travel. The handling is actually good but I wanted to tweak it some and try to get as much of the harshness in the ride out as I could. When I do the front I think that will complete the package. Thanks for your help and anymore comments are appreciated.

Noise, vibration, and harshness tend to be somewhat subjective in measure and are typically tough to make compatible with precise handling on our old heaps. To me, rubber is very mushy and poly bushings are very comfortable, but I've driven competition cars that used nylon or bronze bushings that produce a harshness that most people wouldn't tolerate.

Things that contribute to NVH are poly bushings, high spring rates, high pressure shocks, or stiff and/or short sidewall tires. Since you have relatively soft rates (assumption since you said standard rear springs and I don't know what t-bars, but again, assuming stock) and Monroes tend to be somewhat conservative in pressure (even their HD units), I could only suggest that the poly is what's contributing to the harshness. Even though you have a 50 series tire, most of these are S or T rated which means they tend to be somewhat softer in ride. Certainly more so than a 35 or 40 series, but not nearly as much as a 60 series. Also, 295 on an 8" rim is really pulling the tire in a fair amount. If your running these at 35 psi, I'd be willing to bet you aren't putting all the tread face down on the ground and the pressure is pumping up the sidewall a fair amount, so that will also contribute to NVH. Dropping pressure down to 28 will improve the footprint while reducing harshness.

Can you still get decent handling by using rubber, sure, it will give up some performance when pushing the envelope and running the ragged edge, but if you're primarily cruising, it will be more than sufficient.