Factory stereo stolen! - Need help for replacement

So I just bought an 88 Nissan Pathfinder from my neighbor, (he had 2) but about a month ago, someone broke in and stole the factory stereo. They ripped it out of the dash breaking the wiring harness and antenna plugs in the process. I would like to install an aftermarket stereo into the dash, but am faced with a bit of a challenge with the built-in amplifier. What are my options for installing a new head unit? Do I try to salvage the amp? Should I disconnect all of it and use the stereo's amp? Will I need to run new wiring if I disconnect it? As for the antenna, should I buy an aftermarket replacement, or should I try to find one at the junkyard?

I have searched the web trying to find a wiring diagram to maybe salvage some of the existing wiring or what-not, but all I can find is wiring harness adapters and forums with people saying what a nightmare it is to install a new head unit! Any suggestions would be great, and all will be considered.

Thank You in advance

I installed a new head unit in my 95, leaving the factory amp and wiring as is because its too cold to deal with ripping panels off and rewiring speakers.. .one day i will just re run all the wires from the deck to the speakers. For now i am stuck with a loud audible hiss whenever the music is quiet. . . :(