The only way to make a good decision going forward is to find a machine shop and get an estimate for evaluation (bore measurements), needed machining work and and welding that crack. A competent TIG welder knows how to repair aluminum castings. Good prop shops do it every day on lower unit housings.
Used complete packages are available, but they are used and may be worse than what you're looking at. And you'll know what you have when you're finished. Done right, this motor will last a long time.