Here are two photo's of a twin cam engine (this is from an Elan, but you will get the idea). The hole in the bottom of the head connects to the block via a short rubber fitting. It is possible to install with the engine in place, but it's a bear to do.
The hole on the side of the head either connects to the airbox via a fitting coming off the head and length of rubber hose to the airbox, or on early cars this hole is for a drain tube that runs to the street.