the alpha has a water pump/impeller inside of it, the bravo does not and requires an external pump.
Yeah I know, mine does too. But I still think you need to run a normal "automotive" style pump to recirculate it. I think mercruiser calls it a recirculation pump. Mine is an alpha, and it had one stock and I'm still running one along with a thermostat too. But idk for sure if its a required thing.
I've been researching swapping my manifolds for the newer style and going with thru hull and cooling is the big thing I have come across. In regards to water lines and etc.
In other words idk if the impeller in the drive is enough to keep the engine cool. But it might be. Just thought I'd give you a heads up.