I swapped an 87 5.0 and t5 into my 92 4 cyl. auto.
I want to say 91 harness is different from the 92/93, and 87-89 harnesses. I found a 93 harness and maf when I did my swap.
But you might need to find another 91 5.0 harness. Unless you want to swap the interior wiring out too.
Your o2...