check the fuel pressure
then check the codes

Can almost guarantee its not ECM if it starts. If it took 20 minutes to start and relays were clacking, then maybe ECM. Even a 318 ECM on a 360 should satrt and idle very nicely, just not pull hard.

318 ecm in a 360 is a problem that should be fixed- BUT 89 360 ECMs were a one year only computer (14 pin and 60 pin connectors)