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The Ford rotor *hat* is shorter, the overall height of the Ford rotor is only 1/4" more than that of the W rotor.  The Impala rotors bolt circle is 118mm (4.6"), the W rotor is 115mm & the Ford is 114.5mm (4.5"). The Ford rotors pad surface thickness is near identical to the W rotor thickness 1.040" vs Ford 1.101".

Oh, I didn't know about the J-bodies having the same radio, but it makes sense.  I think some 3rd-gen F-bodies used the same radio as the Grand Prix. I'd read the same thing about the amps on the GMT400 forum while searching for info on these, as I'd wondered if I could just replace my CDM module rather than repairing it, but ended up deciding that'd be pointless as probably all of them need those capacitors by now.  Anyway, I can confirm the amplifiers are 100% the same between the non-EQ and 5-band EQ models.  There is no difference whatsoever between the amplifier stages.  They're both using a pair of Delco DM165 2-channel amplifier ICs.  In fact, I used my 5-EQ CDM (from GP radio) as a DM165 donor for my non-EQ Cutlass radio because one of its DM165s was blown.  There's only one difference between the non-EQ and 5-EQ models and that's the presence of the EQ IC.  In the non-EQ model, there are shorting jumpers (yellow arrows in the image) to connect the EQ input solder pads to EQ output pads. That said, there is a newer CDM with different amplifier ICs.  You can tell them apart because the amplifier heatsink has vertical fins instead of horizontal.  It's very likely that one does have more powerful amps.  In this pic, top is old (like I have) and bottom is the newer one. The GMT400 thread did mention the old and new style are completely interchangeable. They communicate via E&C Databus, which has been somewhat hacked. https://stuartschmitt.com/e_and_c_bus/ I think Tech 1 and Tech 2 have the ability to read it with the right cartridge and cable. If it uses a CDM similar like the top one in the previous pic, then I'd bet on it.

I have for 24 years used the nylon pad/blocks and have had no problem. I bought and installed the rubber pads with the 3-M adhesive after cleaning them  while a new rack unit was being installed. They didn't stay in place so I bought the nylon pads which lifted the car back up to a nice stance. I did grease the ends of the leaf spring. I have zero complaints and have had the car for 27 years. I replaced them once and I bought an extra pair and should install them again.

The factory radio is cutting in and out on some of the speaker channels in mine as well. I’m sure it’s some caps going bad.

Apparently, they are a lot more common than we may realize. Any 2 piece HU like yours used those radio modules. The 88-94 Regals, the early GPs, Sunbirds, 88-94 GMT 400s etc…There were also a number of variations of them, based on whether there was just bass and treble controls or the 5 band eq, as well as whether they were equipped with AM stereo capabilities or not. I’d venture an educated guess that every OBD1 GM vehicle with steering wheel controls is just about guaranteed to use one.    On the GMT400 front, I have heard that the modules intended for the 5 band EQ models also have a higher power amplifier in them. I tend to believe that, based on my experience with my Regals   Pretty sure those also have some sort of databus that is accessible via a Tech 1. There are troubleshooting steps in my Regal FSM that allude to using bi-directional controls on a Tech 1 to monitor and control some of the radio functions for troubleshooting purposes.