Word of caution to all of you guys think a few hours of freezing temps nothing to worry about. WROOOONG.
While the block can withstand a few hours of freezing temps, there are a lot of smaller water routes, IE: exhaust manifolds that have little water in them. water pick ups, drives, hoses, pumps and even temp. sencors. Depends on how fast temps will fall, will depands how fast water will freeze and expand, thus cracking things, may be not the block but items you may not see any problems months or years down the road. (water) For the salt water boaters it's les of a problem due the the freezing temp. of salt water.
Generally the block and drive will be the same temps as the surrounding air temp. It will take some time for the block and drive to get cold enough to freeze even if the temps go bellow 32 for a while. But why take a chance. I moved from Chicago and I was late winterizing one of my boats around Thanksgiving, Temps dropped, manifolds cracked, Didn't know untill the spring even when I winterized soon after. You guys had no issues,!? (that you know of) are lucky. Count your blessing and be ready. When I winterized I even draind the mechanical speedo lines and removed the outdrive.
Food for thought.