Do you have any pics of yours, I'd love to see it?
I had one hell of a time with mine when I tried to put in a CD player, all it had in it was an AM radio, took over 7 hrs to take it out and install, I had to take the whole front dash off and rewire the speakers, I put a pair of 6x9's in the back too since there were no speakers back there to begin with.
this is the only pic i have of it right now......

the entire drivetrain came outof this.....

wiring in the computer control system was much easier than i had expected. it only took 7 wires from the EEC4 into the stock 78 wiring.
for hvac, i installed the entire hvac box from the gt into the fairmont. the pedal assemblies were a direct bolt in while the dash was out. for the radio, i installed the stock 89 mustang premium sound system, complete with rear deck speakers, the 2 dash speakers, and although i haven't wired em yet, i installed the 2 door speakers too.
i installed the mustang carpet, and front seats, but the 89 center console wouldn't match, so i used one from an 83 mustang. the rear seat will be re-upholstered to match the fronts, and i'm making a new headliner right now......and repainting all of the plastic trim either black, or the factory grey.
i drove all the way up to hershey pa for a good dash pad($150 for the dam thing) and a nearly perfect rear bumper, along with those rear interior plastic trim pieces.
i still have to handle the rust on the 1/4 panels, but that window sticker stays.

i haven't been able to find anything with a cowl for a fairmont that i like, so i'm gonna try to find a junkyard hood, and try to make my own cowl hood....i want to go 4" like the mustang was, and move my gauges out there.
it's taking me forever, but if i ever get her on the road, it'll be worth it. i can start driving it tomorrow if i were to register it, but i don't wanna drive a partially complete car.....
almost forgot. the engine install was crazy easy, as i simply swapped out the k-member, along with the entire front suspension, and steering. since they're both "fox" chassis, virutally everything was a bolt in.
i was gonna cut the trunk to make a stock mustang fuel tank fit, but i wanted it to look like ford built this car with fi, so i had a stock fairmont tank modified to accept the stock type electric pump.