Leaking Coolant

While I very rarely ever post, I use FABO constantly as a "search tool" to learn. But this time I have a real problem and would appreciate some feedback and recommendations. The engine is a 318 and was built by a local person here in the SD area. It is a 318 block with 273 heads that have been ported etc.... by the engine builder. I think many of you know him and most seemed to respect his input concerning Small block engines. That is why I choose him.

The issue is that I was very close to breaking in this motor. Two days ago I added the Coolant/Water to the radiator. One day I added the first two gallons of mixture but didn't have enough, so the next day I added the rest to fill it up. Yesterday when I went out to the garage I noticed the floor was wet under the left side of the engine, about mid way back and under the starter area, or back corner of engine. Also about a 1/2 cup came out of the oil drain hole. It didn't leak until the radiator was full.

Now I'm very worried and have no local support to come through the issue and hope this forum can point me in the right direction. Do I add more water and attempt to detect where leak is from? Do I break it down and see if it is intake gasket? Go deeper and see if heads are torqued correctly. I also have Dougs that were installed by a local exhaust shop but I checked around these studs and all seemed to be dry. If a exhaust stud was leaking would it allow coolant to get to the base pan? Is the engine being damaged because it has coolant leaking through to the base? I really could use some solid input so I can correct the issue and move forward. Thanks.