First thing: check compression. That will tell you if you have any seal leaks. If it is all well, you should be good. Nothing else is really complicated about the motor. About 100 lbs (95-110) is normal on the 13B. There are 2 spark plugs per cylinder, you only need to check one.
I would grab new thermostats also. The ones for the 13B ran either 180 or 195 degrees. Mine were out after a few years sitting. New spark plugs would be a good idea also.
I have 2 Holley 4 barrel carbs on the 13B's (they are in my new project boat, a 42' Chris Craft) and as long as you have a fairly well tuned carb, any should work on your 12- I get about 175hp each. So, if that carb is shot, just about any after market will work just fine. It isn't rocket science.
If you have any other quwestions feel free to ask!
