New Header Bad News, Need Advice Please

[907mge]

So the problem is:
I went down to pick up my 1990 n/a at the exhaust shop where the header was extensively modified to fit and installed. They had to bend the down pipe and lengthen the O2 sensor wire which the location is now right in front of the cat.
So I started it and let it run for a minute or two, to warm up a little. Then I was playing with the throttle a little to see how it sounds. That’s when it went wrong, it died. I restarted it and found it easy to start but now running very rich(lots of black smoke) and really rough .
So my thoughts are that the o2 sensor might have got fouled by the burning of the paint because I had repainted the whole header before it was installed. I will be going back down to the shop tomorrow since the car is stuck there. I’m just trying to get some advice since I want the shop to look at it before I start messing with it. I did not disconnect the o2 sensor since it was hard wired in. That was my first thought. So any help is much appreciated, Thanks.