It will be operated by one of the RR-powered Virgin Atlantic B747-200s that have recently gone to Air Atlanta. Although Air Atlanta will be operationally responsible for the flight (since Virgin's future fleet won't have a spare B747-200 for the summer only MAN-MCO flight) it will be crewed by Virgin pilots and cabin staff.
The only thing I'd check with Virgin reservations is whether the aircraft will have PTVs. I've heard conflicting reports, and they may have been removed by Air Atlanta on cost grounds.
If I were you I'd look into flying bmi british midland via Chicago or Washington. Not only will you support the airline and their new services, all reports I've had about bmi's service on the A330 have been excellent, but you get the chance to sample a United 737/757/A320 on your flight down to Orlando.