IMO too much effort...
You'll need:
All of the "Upper end" of the '86/'87 motor; intake, throttle body, and sensors
The '86/'87 headers, and crossover pipe
'86/'87 Turbo with oil return, and oil feed line
All the brackets, the tensioner, the alternator, *Power steering
Wiring harness unless your a glutton for punishment like me
*Converting the '86/'87 power steering to work with the '84 brake system is going to be "fun."
You can use the '84 injector harness.
You could use the '86/'87 oil pump and then have to use the '87 radiator, oil coolant lines, and '87 radiator hold down.
I'm currently installing an '87 T motor into my '84 GN.