If you can find a ECU on a 89 Wag I'd like to see it.
The ignition modules should be the same, provided they are Ford Dura Spark2 systems.
The main hitches are.. the flywheel from the 304 will bolt onto the 360 but it will shake you to death, AMCs are balanced off the flywheel, so you need a rarer 360 flywheel (if running a manual tranny) otherwise the flex plate from the 360 will work fine.
Second is you have to keep the 304 exhaust manifolds.

Thats it.

Have fun.

SD