failed smog

[osaltyone]

Well...I took it in today and HCO was 128 and max allowed was 98 @ 25, was right on the nose for passing at 15. He also wrote Tampered on my slip because my o2 sensor was unplugged and he could not find the wire running to it and aparently my timing was 14 BTDC when he checked it. Should I take it to a smog repair place? The cat was replaced 2 yrs ago because it failed.
Anyone know where the o2 sensor plugs in on an 84 with a 305.

The truck was my dads project and after he passed, I took it on, but know very little about the emissions/engine. I have tore the whole suspension out and bagged it, so I can work on them.