You are going to need an Alpha ECM. The wiring harness is the same, plus you will need the parts on the shift bracket that are missing between the two.
Not 100% sure but you may need an alpha ecm for the shift interupt. I know the bravo ignition module on the carb'd ones dont support the interupt. Merc lists an ECM for each alpha open and closed cooling and bravo open and closed cooling and 2 differen version of each