Yes, you can have WS-SUP720-3BXL as redundant sup, like below:
od Ports Card Type Model Serial No.
--- ----- -------------------------------------- ------------------ -----------
4 4 CEF720 4 port 10-Gigabit Ethernet WS-X6704-10GE SAL12345ABC
5 2 Supervisor Engine 720 (Active) WS-SUP720-3BXL SAL23456ABC
6 2 Supervisor Engine 720 (Hot) WS-SUP720-3BXL SAL34567ABC
9 24 CEF720 24 port 1000mb SFP WS-X6724-SFP SAL45678ABC
Tom
