new here need some suggestions

i have a 1989 240sx se. it had the ka24e orginaly under the hood i threw one rod out of each side of the black. i have since bought what i believe to be a 93 ka24de. i wanted to put the twin cam in the car instead of another single but now its looking like i need a new wiring harness and a computer should i just find a good single cam block since my head and everything is still good or switch it to the twin cam. i wouldnt say im mechanicly declined i just know general mataince and fixing