Hi Matthew,
Chess960 preserves the genuine asymmetrie of Chess, thus its castling
rules make sense, overmore thus becoming also a superset to traditional
chess.
But there is Chess480 with 'modern' castling (King makes two steps if
possible). But Chess480 with 'symmetric' castling, as you proposed, is
not yet a common variant.
Nevertheless you could play all those three variants at the SMIRF chess
engine and GUI. This is also true for the 10x8 board geometry.
http://www.chessbox.de/Compu/schachsmirf_e.html