Believe it or not I found those bolts in the pool of oil. I have the LIM off and that gasket replaced. So I'm just waiting on the upper now. Then where the coolant block drain plug is. Going to change coolant, seafoam it, change the oil, and put in new spark plugs.
What I've been able to find is that there are two block drain on the SII 3800. One front and one back. The manual says that these are normally not removed for cooling system service or flush and are difficult to remove and replace.
You just may want to play with those and carry on with the build up.