Andrew is correct. It is a replacement engine. Over on the Chevelle site I was told "CE" stood for Chevrolet Engine. I have always called it counter exchange as well. I didn't argue it, because we all know what the engine is. The heads should have accessory holes. They look a lot like a 305 casting , except the humps are larger. Sorry the engine is not original to the car.
1969 x-77 Z/28 orange/ white stripes, named by my daughter "Clementine ", M-22 close ratio, 4:10 12 bolt, CE 302. Hugger orange with white stripes. White standard interior. Restoration complete May 2018