'77 Aspen had A/C, which I've removed. I bought the non-A/C water pump pulley, removed the extra crank pulley and changed out the P/S pump brackets to the non-A/C variety...then came the trouble.

The P/S pump (same P/S pump as with A/C, never changed) sits too far forward when mounted to the non-A/C P/S pump brackets. With the A/C setup, the P/S pump belt rode on the forward-most pulley groove, and with the non-A/C setup, it's supposed to ride in the rear-most groove. The donor vehicle was a '76 Aspen, so they are the correct brackets and pulleys.

Are A/C and non-A/C P/S pumps different?

I doubt the "pump" is different. The same pump is listed as fitting most everything mopar from 75 to about 79. Now the pulley that is pressed on to the pump could very well be different for different applications. When you buy a pump it comes without a pulley, you have to reuse your old pulley. The pulley takes a special remover-installer tool, usually available from most part stores with a loan a tool program.


TopHat

With the 60's A-Body cars, the PS pump bracket spacings were also different. (and the pulleys have different depths, as already noted)

It is alwaya a pain trying to mix & match parts when adding or subtracting belts to the system.
DD

Yes, I've got a pulley puller and even took a pic of the donor car's setup before I removed it, so if I need to, I can remove the donor car's P/S pulley. I wasn't anticipating the P/S pump mounting location to be an issue with the new brackets, but it is.

Parts America does list a different part number for both A/C and non-A/C in one brand, but the same number for both in another brand- not much help there.

Thanks for the comments so far. I'll get it figured out this weekend.