I would like to offer a word of caution. Running antifreeze through a raw water cooled motor with Pauls setup is fine as long as the engine is hot and the thermostat is open. Often in cold weather along with colder water temps it can take a surprisingly long time for the thermostat to open. When the thermostat is closed, some raw eater cooled engines operate in by-pass mode meaning that the raw water is circulated only to the oil cooler, exhaust manifolds, risers and then exit the boat through the exhaust. In this mode the water in the block remains uncirculated until the thermostat opens. Many of the older engines do not have thermostats (like Pauls CC Hercules) and thus there is no worries about running coolant through the motor and having the antifreeze reach all the wet areas of the engine. Much depends on the design of the cooling system. There are many different variations of cooling systems, especially with the older engines. Be sure you think it through before assuming that coolant has reached all the critical areas. In such cases I will pull off the thermostat housing, remove the thermostat and place a large funnel in the opening and pour in the antifreeze. This assures the coolant has reached the block.
I will also offer that I highly recommend using antifreeze for winterization rather than simply draining the blocks and manifolds. A drained engine will always remain wet. This combined with the greater exposed surfaces to oxygen, rust will more readily accumulate. I have seen some rather dramatic examples of older motors that were simply drained every winter verses engines that used some form of antifreeze.