It is an 89. I installed the 91 abs system years ago. I did a write up on the series one swap, and would suggest that if you are not looking at building the motor above 300 hp. The series two is a lot more work and modifications.
My first guesses are ICM or CPS.
Second. If you have used fuel treatments such as seafoam or a few others, I would replace the O2 sensor. Many times they don't send a code.
I know some are corrupt, I can't fix that.
Grab them before someone realizes what they are.
https://drive.google.com/folderview?id=1j7rhZNXzdzuyFkpsbYrzs9aEoyK7w6dt
Probably two separate issues. The cruise is most likely the cervo, or the vacuum line to it, assuming you have power to it.
Mirrors I would check for power at the controls first.
If you install a relay in the initial head light circuit they work fine
Some times the will stay on for a minute or so, but I find that nice when in a dark area.
I installed mine in the interior relay area with a couple wires from a donor caddy
Yes pull the wheel, you will need a lock ring compressor and a steering wheel puller. About $30
Buy a replacement lock cylinder, and not a cheap one or you will be doing the job again soon.
https://m.autozone.com/emission-control-and-exhaust/catalytic-converter/magnaflow-catalytic-converter/888043_64788_2149?aqs=
Pretty easy. Two bolts and a clamp. Just keep a long extension and universal joint handy, as they will keep the cussing to a minimum.
I would pick up a 94-95 series one supercharged motor. It will run about the same cost. The only additional cost would be the 5/8 heater hose, extending the injector plugs, memcaler and tuning.