Cam Cover, Phase 1 LT5 Prototype.  A seriously collectable LT5 part, not likely to ever see one for sale again. 

This is a raw casting, with no machine work.  The under side is marked in black felt tip "Not Heat Treated."  It came from Rick Kirk's LT5 hoard, after Rick passed away. There is no telling how or when he got it, except that it surely came via Mercury in Stillwater, Oklahoma.