rear axle is moving side to side...

Good question and I don't know the answer. I would think with an adjustable panhard bar (not just the length, but vertically, i.e Maier's PHB) you could match the roll center of the springs and the PHB.
The question is, why would you want to run a PHB and solid bushings?
Most of the lateral deflection in a leaf spring set up comes from the bushings and shackles. That is also the source of roll deflection. When you use solid (Delalum) bushings, you control both lateral and roll deflection. The only way the body is going to move laterally with solid bushings (and stronger shackles) is through the springs themselves. How much do you think your springs are going to flex sideways?
If you use rubber bushings, the bushings flex side to side, so you need a PHB, The rubber bushings also flex in roll so you need a sway bar to contol that. In theory you would have a more compliant and adjustable suspension. You may have to adjust the size of your sway bar and location of the PHB for optimal results. Improperly set up, you may end up with binding or oversteer.
Maier is the only one that sells a 65-70 specific PHB. They recommend rubber bushings and sway bars which they also sell.
Global West does not have PHBs or rear sway bars.
Two different schools of thought. Each with pros and cons.

Depends on what you are trying to achieve

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i remember now, it's called roll center migration. when you go throught a corner the roll center of the car changes from one side to the other and the height of the roll center goes up and down. with a PHB you have one roll center and with the del-alum bushings you have another so you end up with conflicting roll centers which can result in binding and other problems.

the del-alum bushings will allow a smoother ride on the street but they will transmit more noise and vibration so it's kind of a trade off, but the moise and vibration would be minimal especially when you consider that you'll have better handling and a smoother ride. a panhard will also transmit noise since the rear end is now basically connected to the body with a solid link and either poly bushings or heim joint ends but will not change the ride quality at all while the del-alums will offer a smoother ride.

since this is primarily a street car i'd go with the del-alums. were it a track car i'd go with a watts link or the PHB if cash was an issue.

66Runt said:

HD is heavy duty. If you look at the side plates, they are much thicker than stock, and the grade 8 fastners reduce flex. The overall effect is less lateral movement.

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Thanks. I've always wondered if there was an HD shackle with the two plates connected that would fit our Mustangs.