Tqmatch -
Of the aircraft used on the DHFS contract at RAF Shawbury, IIRC we did not operate with both floats & winch fitted. Although those aircraft are BB and not B3, I would assume the physical hardware is the same.
In fact the other way round - we did not operate over the water when winching WITHOUT the floats. This is what happens when the button (manual activation only but VERY sensitive) is touched, but you will note the winch is also in the winching position. It would be out for winching but retracted (almost) flush against the fuselage when not in use, as shown in HeliHenri's photo.
Student strikes again
There only four or five ac fitted with the winching kit (750-755 IIRC) which were also the only ones we could fit with the floatation gear, although the winches and/or floats were only fitted when the winching detachment was coming up. Apart from some wiring mods and a special compwash fitting I don't think there were any other differences from the stock BB.