904 cable replacement '65

The reason you don't want to remove the cover, is the spring hooks onto the park pawl. If you remove the cover, and pull it down, you will streach the spring, making it hard to reinstall. If you can't remove the plug in the housing to release the spring, unbolt the cover, and carefully lower it slightly, so you can reach in between the cover and the case with a small screwdriver, and release the spring from the cable. Then you can lower the housing.
To install properly, you MUST get the cable loose from the housing. Then reinstall the housing onto the trans, then install the cable into the housing. It is next to impossible to install the spring and cable adapter while the cable is in the housing.
PS: If you look at the pictures of the spring in the link above, the free end looks like it has been streched out of shape. It is supposed to go into a hole in the pawl, and hold the adapter to the pawl.