So, this website introduces Chess 744 and addresses the confusing castling issues of Chess 960. Basically, we removed the Chess 960 setups with rook and king in a corner and then used the exact mechanic from standard chess. Rool moves to king (if not already adjacent) and then king swings behind the rook. Here is the site - along with a designated setup for each calendar day. https://sites.google.com/view/chess-744/t…
The mechanic for standard chess is:
(If Rook and King have not moved (and no funny business with pawns promoted to Rook), and none of the three spaces the King is involved with are attacked, and all the spaces between the King and the Rook are unoccupied) King moves two spaces, Rook moves to the space the king passed over. The order is important, at least in tournament play.