LGW - MCO on a LHR 747?

I have seen somewhere on this board that the VS 27 & VS28 flights between April 28th and May 15th will be operated by a LHR plane.
Does anybody know if this applies to each of these days or does it get decided on the day?
I am booked on my first ever UC flight midweek and I would certainly be very happy if I'd get a LHR 747 as an added bonus.

A LHR400 will be operting the LGW-MCO inclusive of these dates while the LGW400 go in for there routine maintenance.

I have also heard a second LHR400 will be coming to LGW for short while not sure which flights it will operate or the dates yet!