Here is one of the better write ups I have found regarding putting an aftermarket HU with the 460. Hope it helps
Integrating AM Head Unit w/ Mach 460 - Corral Forums
Plus a few other misc. stereo related articles:
Subwoofer Install with Mach 460
Mustangworld Subwoofer install to Mach460
Speed sensitive volume control
Speed Sensitive Volume for your Mustang - StangNet - The Mustang Network
XM Radio Install
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Steering wheel radio controls
Mustangworld - Radio controls Mod