bigbearmustang28

I stumbled on this forum in hope of some help with my project. I came upon a 1988 5.0 V8 that was completely rebuilt and had low miles and have recently swapped it into my 1987 mustang. It seems to run okay ? problems I am having are the engine harness was all cut up so I did my best to repair it per a haynes manual, but when i took it to a reputable race shop in socal they put a scanner on it and said I was missing sensors and that was causing it to run very rich, not sure if the 02 sensors are messed up now but they did not list what was missing as they said they could not tell from the scan. What would be the best approach in starting to hunt down what I am missing ?Thanks in advance.