OK, I found a photo of the front of the block on the internal bypass engines. Found this photo in Allan Faust's photo bucket. Thanks Allan !
http://smg.photobucket.com/albums/v395/joker77/Engine%20-%20Drivetrain/?action=view¤t=head014.jpg
What are Welch Plugs you ask? They're also known as freeze plugs or frost plugs. Here's a welch plug ralphing up rusty sludge buildup in the block that could be contributing to your overheating problem. Drive an old screwdriver into the center of one of yours near the back of the engine on the drivers side and see what ya find in there.