I am hoping my process worked and maybe someone will be able to tell me if it should. But instead of the bolt type plugs on the side of the block, I have brass drains. I drain all the water out and close them up, disconnect one of the lines at the thermostat housing, hook up a 4 foot section of hose with a funnel on the other end, elevate the funnel so there is velocity of the antifreeze into the block and keep pouring it in until it comes out of the ports at the back of the boat. I just hope that the water that couldn't drain out got mixed with antifreeze. Any speculations?