There should have been no need to change out the dash wiring harness. The N/A and XR2 dash harness should be the identical.
Now to the fun part…..
Did the donor car run before pulling the engine?
You swapped the ecu and engine wire harness, did you take the XR2’s ignition knock box off the firewall too? Without it, you won’t have any spark.
Does the engine try to crank over when trying to start the car?
When you turn the igniton switch to the on position before trying to start the engine, do you see the check engine light?
If you do see the check engine light, have you tried checking for any codes?