Most Fox's were amplified, so it would probably actually be a Metra 80-1771 harness. I work at Circuit City in the Roadshop (car audio), so i deal with this all the time. The radio will be a piece of cake to take out and put a new one in. I'd personally go somewhere that sells Metra kits and harnesses cause they fit so much better than scosche.
BTW- If you want the amp to be bypassed, then yes, the 80-1770 harness will work, you just have to find where it is plugged into the amp behind the radio. Sorry for any confusion.