Just a correction to Real1's definition of a 427 SO. Late 406's and all 427's have cross bolted main caps for racing durability. The center oiling galley used in all FE engines proved inadequate for racing endurance. So, in 1965 the 427 block was a new casting with the main bearing
oil gallery on the side. This gave the mains priority in the oiling system and greatly increased the 427's ruggedness. This side galley casting is the sure identification of a 427 SO. I do believe, however, that some service blocks show this casting but are not drilled and use solid lifters.
Tim