The two threaded ports on the top of the manifold are water jacket ports. Put a gauge in one and a schrader valve in the other, pressurize to 5 lbs. (others prefer 20 lbs. but I don't see why) and see if the pressure holds. Alternatively you can plug one port and buy this in the Home Depot plumbing department.
edit: I want to add that the only thing worse than having a cracked, non-viable block is finding out about it AFTER you've invested considerable time and money in a rebuild.
edit, the sequel: If I were in your shoes I'd focus on getting the head studs replaced and the head reinstalled first, then perform the pressure test before doing anything else. A little birdie whispered in my ear that he noticed you lifted the engine by the lifting eye/alternator bracket. That is perfectly understandable BUT we have learned the hard way lifting thusly may cause another problem, a crack in the head underneath the lifting eye. The pressure test will check that too. Have a squirt bottle of diluted dish soap (3:1) handy to spray over the engine when it's pressurized. Any breaches will form bubbles.
Check out this thread:
http://www.moyermarineforum.com/foru...015#post114015
A few years ago I acquired a used Atomic 4 from a guy who went electric. It was a Southern California boat so no risk of freeze damage but still the very first thing I did was the cooling system pressure test. It held pressure for 1/2 hour so I knew I had a viable block, head and manifold.