Otherwise this stone would seem defaced beneath the translucent cascade of the shoulders
Here, we have another "Otherwise," so just remember what we're originally referring to—the statue's inner light, which leads to its inner life.
So, if the statue didn't have its own internal illumination, then it would seem mutilated and "defaced," but since it does seem to offer its own light, it doesn't look disfigured at all. Got it? The "translucent" quality of the stone (as if it allowed light to pass through) suggests the clarity and illumination of the marble statue's pale beauty, while "cascade of the shoulders" makes us think of powerful muscles and masculine strength that would seem to fall ("cascade") away from the neck toward the back. This statue is seriously ripped.
and would not glisten like a wild beast's fur:
Following along those lines of strength and animal magnetism, the statue's gleaming torso also seems to have a quality of wildness, since it "glisten[s] like a wild beast's fur." This is a simile. It isn't to say that it actually has fur (that would be a statue of a wolfman, not a Greek god)—but something about it suggests that it's like a wild beast. The statue, even in its incomplete state, emits an untamable power.
Now, before you go to the last stanza, we'll just note that any rhyming here—end, slant, or otherwise—seems to have gone out the window in this stanza. We do get a bit more iambic pentameter in line 11, though (see "Form and Meter" for the details).